Journal of Bioscience and Bioengineering

VOL. 107 No. 5, 475 – 487, 2009

www.elsevier.com/locate/jbiosc

REVIEW

Lantibiotics: Diverse activities and unique modes of action

Sikder M. Asaduzzaman,1 and Kenji Sonomoto1,2,⁎

Laboratory of Microbial Technology, Division of Microbial Science and Technology, Department of Bioscience and Biotechnology, Faculty of Agriculture,
Graduate School, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan 1 and Laboratory of Functional Food Design,
Department of Functional Metabolic Design, Bio-Architecture Center, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan 2

Received 3 September 2008; accepted 9 January 2009

Lantibiotics are one of the most promising alternative candidates for future antibiotics that maintain their antibacterial
efficacy through many mechanisms. Of these mechanisms, some modes of activity have recently been reported, providing
opportunities to show these peptides as potential candidates for forthcoming applications. Many findings providing new insight
into the detailed molecular activities of numerous lantibiotics are constantly being uncovered. The combination of antibiotic
mechanisms in one lantibiotic molecule shows its diverse antimicrobial usefulness as a future generation of antibiotic. Since
lantibiotics do not have any known candidate resistance mechanisms, the discovered distinct modes of activity may
revolutionize the design of anti-infective drugs through the knowledge provided by these super molecules. In this review, we
discuss the rising assortment of lantibiotics, with special emphasis on their structure-function relationships, addressing the
unique activities involved in their individual modes of action.
© 2009, The Society for Biotechnology, Japan. All rights reserved.

[Key words: Lantibiotics; Structural variants; Structure-activities; Modes of action; Lipid II; Drug design]

ANTIBIOTICS AND RESISTANCE TO ANTIBIOTICS “weapons” against each other. One such glycopeptide antibiotic,
vancomycin, has long been reliable in treating infections caused by
The discovery of penicillin in 1928 by Alexander Fleming was a bacteria resistant to several other antibiotics, and is usually reserved
historical milestone in human civilization; the subsequent curing of for the treatment of serious infections, including those caused by the
individuals with otherwise unbearable and sometimes fatal infectious “super bug” methicillin-resistant Staphylococcus aureus (MRSA).
diseases by antibiotics has been considered as nothing short of a However, even vancomycin-resistant enterococci (VRE) have now
medical miracle. The identification and production of a wide variety of become quite common (2, 3), and this is made more complex by the
antibiotics on a massive scale have revolutionized medical spread of vancomycin resistance genes throughout the pathogens.
approaches. Unfortunately, the initial wide-spread use of antibiotics Therefore, these dramatic increases in antibiotic-resistant pathogens
has generated a strong evolutionary pressure for the emergence of have stimulated efforts to identify, develop, or design antibiotics that
resistant bacteria. The exclusive reliance on broad-spectrum anti- may be active against multi-resistant pathogen-caused diseases.
biotics has further intensified the problem by inducing the develop-
ment of multi-resistant pathogens. One notorious example is that the DO LANTIBIOTICS SUPERSEDE CONVENTIONAL ANTIBIOTICS?
vast majority of the clinical isolates from Staphylococcus aureus strains
have been found to be resistant to methicillin (1). The devastating Some antimicrobials are now being considered as alternative
threats from acquired resistance to antibiotics are compounding from antibiotics, such as bacteriocins, bacteriophages, probiotics, and
all regions of antibiotic end-users. Consequently, there is currently no antimicrobial peptides. The attractive features of some of these
antibiotic in clinical use to which resistance has not developed. The molecules, for example, their natural sources, wide range of activities,
World Health Organization has warned that the rapid increase in ease of production, and the fact that they are not prone to developing
resistance among pathogens may become untreatable (WHO/41. resistance, have interested researchers seeking to develop new
http://www.who.int 2000). Thus, there is a pressing need to discover antibiotics. Among these different sources of alternative antibiotics,
and/or develop new agents that are active even against the emerging lantibiotics appear to be one of the most promising candidates.
resistant bacteria. Traditional antibiotics usually exert their activities via a specific mode
The discovery of new classes of antibacterial compounds based on of action; for example, penicillin interferes with the cross-linking of
targets identified from bacterial genomics is historically invaluable as two linear polymers by inhibiting the transpeptidase reaction and
a source of antibacterial drugs (e.g., glycopeptides) that bacteria use as aminoglycoside antibiotics (e.g., streptomycin) inhibit protein bio-
synthesis by combining with the 30S subunit ribosome, whereas
⁎ Corresponding author. Fax: +81 92 642 3019. tertracyclines interfere with the binding of aminoacyl-tRNA to the 30S
E-mail address: sonomoto@agr.kyushu-u.ac.jp (K. Sonomoto). subunit ribosome and erythromycin prevents the transpeptidation

1389-1723/$ - see front matter © 2009, The Society for Biotechnology, Japan. All rights reserved.
doi:10.1016/j.jbiosc.2009.01.003
476 ASADUZZAMAN AND SONOMOTO J. BIOSCI. BIOENG.,

and translocation steps as a result of binding to the 50S subunit FEATURES OF LANTIBIOTICS
ribosome. Bacteria tend to develop resistance to all classes of these
conventional antibiotics through a relatively simple mechanism. Even All organisms have antimicrobial peptides that act as evolutio-
the antimicrobial peptides derived from many organisms, e.g., the narily ancient weapons. The diversity of these antimicrobial peptides
well-studied peptide megainin, are generally based on their single is so great that more than 1000 peptides have been included at
action of pore formation in the membrane. http://www.bbcm.univ.trieste.it/∼tossi/antimic.html (described the
In contrast, lantibiotics have quite diverse activities; for antimicrobial peptides). Among these organisms, bacteria are
example, nisin and many other structurally related lantibiotics remarkable producers of antimicrobial peptides. Bacterial-derived
(e.g., epidermin/gallidermin) use the cell wall precursor lipid II antimicrobial peptides have a large degree of structural and chemical
bound to the membrane as a docking molecule for pore formation diversity. Polypeptide antibiotics (e.g., gramicidin and valinomycin)
and combine at least two modes of action, i.e., pore formation and are synthesized by large, multi-enzyme complexes from building
inhibition of cell wall biosynthesis, for antibacterial activity at blocks provided by a variety of cellular processes (12). Recent
nanomolar concentrations (4–6). Hasper et al. (7) recently eluci- advances in bacterial molecular genetics have further contributed to
dated the sequestration mechanism resulting from lantibiotic new insights into peptide antibiotics. Ribosomally synthesized
action, which helps to explain how some small lantibiotics that peptide antibiotics produced by certain bacteria are termed as
cannot span the bilayer of the bacterial membrane can still bacteriocins (13, 14). Bacteriocins are divided into classes; lantibio-
maintain a high level of antibacterial activity. Many other tics are class-I bacteriocins that are antimicrobial peptides contain-
distinctive modes of action are currently known to be unique to ing unusual amino acids, such as thioether cross-linked amino acids
lantibiotics, to which there are no known natural resistance in lanthionine and 3-methyllanthionine, and dehydrated amino acids
mechanisms among bacteria. Therefore, we will discuss the in 2,3-didehydroalanine (Dha) and (Z)-2,3-didehydrobutyrine (Dhb)
lantibiotics' molecular mechanisms in order to clarify how these (15, 16). Post-translational modification renders the lantibiotics
molecules carry out their exceptional activities. biologically active. A large variety of lantibiotic structures, biosyn-
thetic mechanisms, and modes of action have attracted significant
THE LANTIBIOTIC NISIN, THE FOREMOST ANTIBIOTIC WITH research interest.
PROMISING FUTURE POTENTIAL Lantibiotics exhibit a number of notable characteristics. They are
ribosomally synthesized, and in most cases the genes involved in
Surprisingly, the history of lantibiotics is older than that of lantibiotic biosynthesis are clustered, designated by the generic locus
conventional antibiotics and dates back to a time before the discovery symbol lan, with a more specific genotypic designation for each
of penicillin. The first lantibiotic, nisin, was discovered in the 1920s lantibiotic member (e.g., nis for nisin, nuk for nukacin ISK-1, gdm for
and has had widespread application as a safe alternative for food gallidermin). Lantibiotics are found on conjugative transposable
preservation chemical reagents in approximately 50 countries for over elements (e.g., nisin), on the chromosome of the host (e.g., subtilin)
40 years, without natural resistance development (8, 9). Research or on plasmids (e.g., nukacin ISK-1). The gene clusters for the
regarding lantibiotics has recently gained renewed interest due to the biosynthesis of representative lantibiotics are depicted in Fig. 1.
emergence of clinical isolates that are resistant to antibiotics such as Although the gene order, complexity, and transcriptional organization
vancomycin, the last-resort drug that has been used against infections of the various clusters differ, three genes (lanAMT) have been
caused by Gram-positive bacteria for almost 30 years. The N-acyl-D- identified that are involved in the biosynthesis of all type-A(II) and
Ala-D-Ala moiety of lipid II is involved in the binding of vancomycin, type-B lantibiotics, and four genes (lanABCT) are present in all type-A
and vancomycin-resistant bacteria thus remain sensitive to nisin due (I) lantibiotic gene clusters (the grouping of lantibiotics will be
to its different binding site (4). Therefore, there has been a rapid and explained below). These essential genes obviously include the
diverse expansion of research activities towards lantibiotics. Despite structural genes that encode the precursor peptides for post-transla-
being the oldest known antibacterial agent, the structure of nisin was tional maturation (prepeptides), which have been designated lanA,
not determined until the elegant landmark studies by Gross and except for subtilin whose structural gene is historically named spaS.
Morell in 1971 (10), and the word “lantibiotic” was just recently coined The lanA genes produce prepeptides that have an extension (leader
in 1988 as an abbreviation for lanthionine-containing antibiotic peptide) of 23–59 amino acids at their N-terminus in addition to the
peptides (11). Therefore, although the history of lantibiotics is very mature lantibiotic. The sequencing of the lanA genes indicates that the
old, a new paradigm is emerging due to their potential and enormous dehydro amino acids in lantibiotics are the result of the dehydration of
applications to meet the future challenges of developing antibiotics serine and threonine residues to produce dehydroalanine (Dha) and
that can combat emerging pathogens. dehydrobutyrine (Dhb), respectively. Lanthionine and 3-

FIG. 1. Biosynthetic gene clusters of some representative lantibiotics. Genes with similar proposed functions are highlighted in the same pattern. LanB and lanC genes of type-A(I)
lantibiotics are substituted by the gene lanM of type-A(II) lantibiotics. Despite the differences in the gene order, complexity, and transcriptional organization of the clusters, three
genes (lanAMT) are involved in all type-A(II) and type-B lantibiotics, and four genes (lanABCT) are present in all type-A(I) lantibiotic gene clusters for biosynthesis.
VOL. 107, 2009 MODES OF ACTION OF LANTIBIOTICS 477

methyllanthionine rings are then generated by intramolecular con- also assumed to be concerned with self-immunity to some lantibiotics
jugate additions of cysteine to these unsaturated amino acids. Though (25). Additionally, two directive genes (lanKR) are often found to be
the exact function of the leader is not yet clear, the suggested possible involved in the regulation of lantibiotic biosynthesis, encompassing an
functions include export signaling, protection of the producing strain important two-component sensory system (26).
by keeping the peptides inactive, and providing scaffolds for the post-
translational modification machinery (17, 18). STRUCTURES AND LANTIBIOTIC GROUPING
In type-A(II) lantibiotics, the bifunctional lanM is responsible for
dehydration and the cyclization reactions. In contrast, in type-A(I) Thus far, more than 50 different lantibiotics have been isolated
lantibiotics, lanB is involved in the dehydration of Ser and Thr to form from Gram-positive bacteria. Lantibiotics are classified by Jung (27) as
Dha and Dhb, respectively, and lanC codes for the cyclase that types A and B, based on the topology of their structures. Representa-
produces lanthionine or 3-methyllanthionine (Fig. 2). The C-terminus tives of the lantibiotic structures are presented in Fig. 3. Type-A
of the lanM enzyme shows 20–27% sequence identity with the lanC lantibiotics are further divided into two subtypes, elongated type-A(I)
enzyme, but it has no homology with the lanB enzyme. Direct and tail and ring region-containing type-A(II), which have different
evidence for the bifunctional role of the lanM enzyme in catalyzing genetic organizations (28). In type-A(I) lantibiotics, the lanthionine
dehydration and cyclization has been provided by in vitro reconstitu- and 3-methyllanthionine residues are formed by the action of two
tion of lctM in lacticin 481 biosynthesis (19). Some lantibiotics also distinct enzymes (LanB and LanC), whereas those that are formed by a
undergo further post-translational modifications. For example, the single enzyme (LanM) are termed as type-A(II). Type-B lantibiotics,
lanD genes encode the enzyme responsible for the formation of AviCys such as mersacidin, cinnamycin, duramycin, and ancovenin, are more
and AviMeCys; it is likely that the epiD gene in epidermin and mesD in globular and compact in structure (29).
mersacidin carry out the in vitro decarboxylation of a C-terminal Cys In addition, a separate subgroup is formed by the two-
residue to form AviCys and AviMeCys, respectively (20, 21). Recently, component lantibiotics consisting of two post-translationally mod-
one of the most post-translationally modified lantibiotics, paeniba- ified peptides that individually have little to no activity but
cillin, has been isolated and identified to show a broader range of synergistically display strong antibacterial action. At the present,
modifications, including N-terminal acetylation (22). this emerging subgroup of two-component lantibiotics encompasses
The N-terminal leader peptide is cleaved, and the mature the structurally closely related lacticin 3147, plantaricin W, and
lantibiotic is then translocated across the membrane. The prepeptide staphylococcin C55, and the completely unrelated streptococcal
of type-A(I) lantibiotics is translocated via ATP binding cassette cytolysin, which combines bacteriocin and cytolytic activity against
transporter LanT, and the leader peptide is catalyzed by serine blood cells (30). The molecular mechanisms responsible for the
protease LanP. However, recent reports of the broad substrate synergistic effect of two-peptide bacteriocins are not clear at the
specificity of NisT for nisin biosynthesis have suggested the secretion present. Generally, the two-peptide lantibiotics work best at
of unmodified, partially modified, or fully modified cyclized nisA equimolar concentrations (1:1 stoichiometry). However, an alter-
prepeptides and non-lantibiotic peptides fused to the leader peptide native classification of lantibiotics has been proposed by comparing
of nisA (23). In contrast to the broad specificity of NisT, the processing the leader sequences of many lantibiotics, which reveals two
enzyme NisP only removes the leader peptide attached to fully different conserved motifs other than those presented above. In
modified nisin. In type-A(II) lantibiotics, LanT has two functions, to this organization (determined by genetics rather than activity
remove the leader peptide and to export the matured peptide. It has profiles or three-dimensional structures), the class I lantibiotics all
an extra N-terminal cysteine peptidase domain, as compared to LanT have a common “FNLD” motif between positions -20 and -15 and
of type-A(I) lantibiotics (24). usually contain a Pro at position -2. The biosynthetic machinery
Some gene clusters contain a second transport system, which involved in the post-translational modifications in this class consists
usually consists of three genes (lanEFG), and is concerned with the of LanB and LanC. In contrast, class II peptides contain a
immunity of the producer strains. In addition, another gene, lanI, is characteristic “GG” or “GA” cleavage site (historically termed the

FIG. 2. An example of the post-translational maturation process of the lantibiotic nisin A. Specific serine and threonine residues (bold) in the nisin prepeptides are dehydrated by NisB.
The cyclization of dehydrated amino acids with cysteine residues is catalyzed by NisC in a regio- and stereo-specific manner, and the protease NisP then proteolytically cleaves the
leader peptide to render the lantibiotic active (for a review of the enzymatic processes involved, see ref. 28).
478 ASADUZZAMAN AND SONOMOTO J. BIOSCI. BIOENG.,

FIG. 3. Structures of a few lantibiotics. A-S-A, lanthionine; Abu-S-A, 3-methyllanthionine; Dha, dehydroalanine; Dhb, dehydrobutyrine; D-A, D-alanine. Based on the topology of their
structures, lantibiotics are classified into three major groups (27), (A) elongated type-A(I); (B) tail and ring region-containing type-A(II); and (C) globular type-B lantibiotics. In
addition, (D) two-component and (E) some irregularly shaped lantibiotics have also been isolated and identified.

“double Gly motif”), contain multiple Asp and Glu residues, and are stability and activity of these antibiotic peptides. The mutagenesis of
usually processed by one modification enzyme (LanM). lantibiotic structural genes has shown the feasibility of changing the
lantibiotic structure by genetic engineering. For example, the removal
of dehydro amino acids, i.e., the replacement of dehydrated amino
ENGINEERING OF LANTIBIOTICS TO DETERMINE THE FUNCTIONS acid residues in lantibiotics with other amino acids, reduces their
OF UNUSUAL STRUCTURES antibacterial activity. The mutant Dha5Ala has activity against
vegetative cells similar to that of wild-type nisin, but the activity
Lanthionine/methyllanthionine bridges are the most notable against spores is nearly abolished (31). The removal of Dha33 by Ala or
features of lantibiotic peptides. These peptides are characterized by the change of Dha5 and Dha33 with Ala leads to a remarkable
their high contents of unusual amino acid residues that form a decrease in activity, to about 1% of the activity of wild-type nisin (32).
thioether bridge to produce lanthionine and 3-methyllanthionine and The replacement of Dha by Dhb and vice versa has been reported for
also contain the unsaturated amino acid residues Dha and Dhb (Fig. many lantibiotics. The formation of Dhb instead of Dha in the
3), which are mostly modified forms of serine, threonine, or cysteine structural region at position 5 of the nisZ gene led to the production
residues. It is now well established, from studies of different of mature nisin Z that shows 2–10 fold lower antibacterial activity
lantibiotics, that these unusual amino acids play a vital role in the (50–90% less than that of the wild-type) against many indicator strains
VOL. 107, 2009 MODES OF ACTION OF LANTIBIOTICS 479

(33, 34). The Dhb10Dha mutant of mutacin II was reported to have TABLE 1. Salient features of some notable structural derivatives of lantibiotics
similar activity (35), whereas the mutant Dhb14Dha did not show any Lantibiotic Derivative Properties Activity Ref.
noticeable change in gallidermin activity (34). The replacement of Dhb Nisin A T2S Dha instead of Dhb Increased 34
by Ala at positions 16 and 20 of Pep5 is found to lower the activity N20P/M21V/ Change in hinge region Enhanced 100
toward some indicator strains (36). The mutant Dha16Ile in mersa- K22T/K22S
Nisin Z S3T Residue for A ring Very low 34
cidin causes a great reduction in its activity against M. luteus and S.
formation
pyogenes (37). S5A Change of Dha to A No production 33
As with the other lantibiotics mentioned above, the two-peptide S5T Dhb instead of Dha 2–10 fold lower 33
lantibiotic lacticin 3147 also showed a dramatic reduction or K12P Reduction of positive Similar 34
elimination of antimicrobial activity, due to mutagenesis in the charge
T13C Additional cysteine Inactive/not 101
lanthionine bridges. Cotter et al. (38) reported alanine scanning residue produced
results that showed that 12 out of the 14 mutations involved in 6 out of M17K K increased solubility Reduced 34
the 7 lanthionine bridges in lacticin 3147 peptides result in N20K Improved solubility Active against Gram- 95
elimination of bioactivity. They also found that changing five negative bacteria
N20E/ Negative charge in Inactive 102
dehydrated residues resulted in a drop in activity. The introduction
N21E hinge region
of a new thioether bridge in the lantibiotic Pep5 results in a dramatic N20V/N20A Change in hinge region Very low 102
decrease in antimicrobial activity (36). The replacement of amino Improved solubility Active against Gram- 95
acids in all positions is not tolerated by the biosynthetic machinery, M21K negative bacteria
and expression does not occur. For instance, an attempt to generate M21K/Dhb / Change in hinge region Very low 102
K22G
the mutant Dhb10Ala mutacin II resulted in no detectable mutacin N27K/H21K Improved solubility Similar 102
production (35), and the change of Ser3, Ser19, or Cys22, which form Influenced C-term. 3–5 fold lower 101
the lanthionines, also results in a loss of gallidermin production (39). V32E charge
Gallidermin A12L Ability to form pore Similar 49
STRUCTURE-ACTIVITY RELATIONSHIPS OF STRUCTURAL VARIANTS disrupted
Nukacin ISK-1 K1A-K2A- Reduction of positive 32 fold lower 41
K3A charge from N-terminal
Due to the importance of the unusual structures in lantibiotics, Fragments and NisA1–12 Rings C, D and Inactive 103
structure-activity relationships have been determined by numerous chimeras E cleaved
studies. Some important structural variants from various derivatives, NisA1–20 Rings D and E cleaved 100 fold lower 103
NisA1–29 All lanthionine 10 fold lower 103
which show a change in the activities and/or properties of lantibiotics, rings retain
are included in Table 1. Lact4816–27 N-terminal 5 10 fold lower 104
Cotter et al. (38) scanned all 59 amino acids of the two-component residues removed
lantibiotic 3147 and found that at least 36 retain some bioactivity and Nis1–11- Chimeric peptides from Similar to nisin, 94
Sub12–32 nisin and subtilin 6–8 fold higher
that some of the amino acids cluster to form variable domains within
than subtilin
the peptides. The glutamate residue in the A-ring of the lacticin 481
subgroup and in the B-ring of mersacidin is conserved and is critically
important for activity, but it has been shown to be nonessential in component (LtnA2) recognizes the complex, leading to a high affinity
lacticin 481 (37, 40). three-component complex for subsequent action (46). An exchange of
the associated mutant peptide LtnA1-Leu21Ala abolished peptide
TARGET SELECTION AND USE OF A DOCKING MOLECULE production (47), and it is noteworthy that a corresponding leucine is
also found in a number of other lantibiotics within the same subgroup
Generally, many lantibiotics (e.g., nisin, nukacin ISK-1) bind to as LtnA1, i.e., mersacidin, actagardine, and plantaricin W. The
the membrane, leading to subsequent action. Nukacin ISK-1 binds surrounding residues of this leucine are highly conserved. In the
the anionic membrane by the lysine residues in the tail region, case of mersacidin, it is found to be involved in lipid II binding (48),
which plays a vital role in its antibacterial activity (41). In the case and the residue may also be related to lipid II recognition for this
of nisin, membrane permeabilization occurs after target recognition peptide.
and formation of a complex with nisin and lipid II (4) for further
action. Hyde et al. (42) reported that the prime target of nisin in TWO-PEPTIDE LANTIBIOTICS WORK SYNERGISTICALLY
inhibiting peptidoglycan biosynthesis is near the cell division site.
Epidermin shares a recognition motif with nisin and binds to both A number of two-peptide lantibiotics (those that synergistically
lipid I and lipid II (5). The activity of nisin against vancomycin- function at optimal concentrations) have been identified during the
resistant bacteria is a result of the fact that nisin does not make last decade, of which lacticin 3147, staphylococcin C55, plantaricin W,
contact with vancomycin's binding site (L-Lys-D-Ala-D-Ala moiety of Smb, BHT-A, and haloduracin are closely related. Lacticin 3147 (Fig. 3)
pentapeptide) on lipid II. Instead, nisin binds the pyrophosphate is a well-studied two-peptide lantibiotic with exceptional antibiotic
moiety of lipid II, allowing this lantibiotic to be effective against efficacy that is achieved when two killing mechanisms are combined.
vancomycin-resistant bacteria (43). The antibacterial activities of It is also effective against multidrug-resistant pathogens such as MRSA
plantaricin C are similar to that of nisin; it that strongly inhibits in and VRE. However, some reports have indicated that its significant
vitro lipid II synthesis and forms a stable complex with lipid II, activities in the nanomolar concentration range are, to some extent,
indicating that both nisin and plantaricin C may target the same strain or species specific. Wiedemann et al. (46) reported that lacticin
structures in lipid II (44). Smith et al. (45) have recently shown that 3147 peptides (LtnA1 and LtnA2) have a very strong synergistic effect
mutacin 1140 causes membrane disruption in the artificial mem- against Lactococcus lactis, but a remarkably weaker effect against Mi-
brane and reported that, although it incorporates lipid II, it is crococcus flavus. Interestingly, the A1 peptide and mersacidin are
arranged in a manner different than that of the nisin A complex. almost equally effective against the lactococcal strain, but their
The two-peptide lantibiotic lacticin 3147 binds specifically with activities differ by a factor of 30 against Micrococcus. The activity of
lipid II in the outer leaflet of the bacterial cytoplasmic membrane. lacticin 3147 involves the binding of the LtnA1 peptide to lipid II. Both
Lacticin 3147 A1 (LtnA1) forms a lipid II:LtnA1 complex and another activities (pore formation and inhibition of cell wall biosynthesis)
480 ASADUZZAMAN AND SONOMOTO J. BIOSCI. BIOENG.,

require the presence of two peptides whose intermolecular interac-

tions appear to be stabilized by lipid II (46).
O'Connor et al. (47) determined the closeness of staphylococcin
C55 to lacticin 3147 and reported that 86% (LtnA1 and C55α) and 55%
(LtnA2 and C55β) of the peptides are identical at the amino acid level.
They also reported that the significance of the relatedness between
these two lantibiotics is so remarkable that the hybrid peptide pairs
LtnA1:C55β and C55α:LtnA2 show activities in the single nanomolar
range, reflecting well with the native pairings. The mutagenesis of the
LtnA1 peptide with the equivalent residues in C55α does not produce
the mutant LtnA1-Leu21Ala. This may be due to the positioning of this
residue in a putative lipid II binding loop.

MODES OF ACTION OF LANTIBIOTICS

The activities of lantibiotics are mostly based on different killing

mechanisms that are combined in one molecule. For example, the
prototypic lantibiotic nisin inhibits peptidoglycan synthesis and forms
pores through specific interactions with the cell wall precursor lipid II
(6). As another example, the mutant [A12L] gallidermin has a
diminished pore formation ability but is as potent as wild-type
gallidermin, indicating that pore formation does not contribute to the
killing of bacteria for this mutant gallidermin (49). It is now well
known that the multiple activities of lantibiotics combine differently
for individual target strains. However, the general steps involved in
lantibiotic activities include i) binding to the bacterial membrane,
followed by insertion into membrane, and ii) the use of receptor/
docking molecules to exert structure-based activity. We will focus, in
detail, on these steps of lantibiotic activities, which are responsible for
their potential antibacterial actions.
FIG. 4. (A) Binding affinity of a cationic lantibiotic, nukacin ISK-1, to anionic [1,2-
dimyristoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt] and zwitterionic (1,2-
BINDING OF LANTIBIOTICS TO MEMBRANE AND dioleyol-sn-glycero-3-phosphocholine) model membranes determined by a surface
INSERTION INTO MEMBRANE plasmon resonance (SPR) biosensor. Nukacin ISK-1 bound to each of the (a) anionic and
(b) zwitterionic model membranes. (B) Dose-response of nukacin ISK-1 toward the
anionic model membrane. Concentrations of nukacin ISK-1 were (a) 20, (b) 15, and (c)
Many studies have shown that membrane binding is the first step
5 μM. RU, resonance unit (41).
in lantibiotic modes of action. Altering the charge distributions in
nisin, for example, removing positive charges from the N- or C-
terminal region of nisin, hampered the initial interactions of the that lacticin 481 (with a net charge of zero) has a higher affinity for
peptide to the membrane (50). By comparing the native nisin with its the zwitterionic membrane than nisin, which binds to the anionic
variants, it was also reported that electrostatic attractions encourage membrane.
the initial association of nisin with the membrane. Breukink et al. (51)
reported that the highly positive-charged C-terminus of nisin interacts PORE FORMATION BY LANTIBIOTICS
primarily with the anionic surface of the bacterial cell membrane. The
same study also indicated a very low association with the anionic Nisin and many other cationic type-A(I) lantibiotics have been well
lipids by the Val32Glu mutant of nisin Z and assumed that the studied in terms of their modes of action involving cytoplasmic and
introduction of a negative charge into nisin Z would result in artificial membranes (4). Numerous studies prior to the late 1990s
electrostatic repulsion from the negatively charged phospholipids. focused on the permeabilization of bacterial cell membranes as the
The strongly reduced binding affinity of a nisin1–12 fragment to anionic primary mode of action of nisin and other type-A(I) lantibiotics, which
phospholipids further indicates the importance of the C-terminus of leads to the release of ions and molecules from the bacteria, eventually
nisin for binding to the membrane (52). Although the initial binding resulting in cell death (55). The pores formed by lantibiotics may have
to the membrane surface seems to involve the C-terminus of nisin, lifetimes of a few to several hundred milliseconds, with diameters of
studies with a variant of nisin Z, in which a short peptide is fused into up to 2 nm (56). The pores of nisin are somewhat anion selective (51)
its C-terminus, show that the C-terminus translocates across the and the pores of nisin and Pep5 work only in one direction (rectifying)
membrane (53). This translocation of the C-terminus is correlated (57, 58), whereas gallidermin and epidermin form nonrectifying
with pore-forming activity, and both the activities are dependent on channels that are more stable (55). The model membrane systems,
anionic lipids. Once it is electrostatically bound, the peptide adopts a such as planar lipid bilayers and liposomes, have a strong influence on
membrane-spanning orientation in which the C-terminus of at least the efficiency of pore formation (59). It has also been shown in
part of the molecules forming the pore is located in the lumen of the monolayer studies that antimicrobial activity is well correlated with
vesicle. However, it is now clear that the N-terminal rings of nisin bind the nisin-anionic lipid interaction (55, 59).
to the disaccharide-pyrophosphate of lipid II, and the positively The two most well-established mechanisms of pore formation are
charged C-terminus initially interacts with the head-groups of the the barrel-stave and wedge models. In the barrel-stave mechanism,
lipids in the membrane bilayer. Nukacin ISK-1 (Fig. 3) also has a net the cationic lantibiotic monomers bind to the membrane surface
positive charge and binds strongly to the anionic membrane, and its through electrostatic interactions and are assembled into a pre-
potential antibacterial activity is crucially dependent on the N- aggregate, and the pores are formed at a certain membrane potential,
terminus positive charges (Fig. 4) (41). Demel et al. (54) reported where the lantibiotic is perpendicular to the membrane (56). In the
VOL. 107, 2009 MODES OF ACTION OF LANTIBIOTICS 481

case of the wedge model, surface-bound lantibiotic molecules bind the orientation of nisin from parallel to perpendicular, with respect
parallel to the membrane surface and generate local strain, bending to the membrane surface (63), and is recruited into a stable pore
the membrane in such a way that the lipid molecules, together with structure (62). The involvements of manifold molecules in the lipid
the lantibiotic, form a pore (60). Chikindas et al. (61) proposed a II-nisin complex are subsequently sufficient to form a defined pore
model for the orientation of lantibiotics in negatively charged of uniform structure (62). Therefore, the lipid II-mediated pore-
membranes, in which the relatively elongated nisin molecule lies complex is highly stable and unique, as other cationic antimicrobial
parallel to the membrane surface with the positively charged side- peptides form pores in the membrane that are unstable, transient,
chains of amino acids pointing out of the lipid bilayer. In contrast with and non-uniform in structure (62, 64). The two-component
this model, which demonstrates the most stable orientation, transient lantibiotic lacticin 3147 has also been shown to utilize lipid II in a
pore formation may result as a molecule passes through the sequential manner to form a defined pore. However, a few
membrane by conformational change. The well-established model lantibiotics, e.g., mersacidin, do not form pores. Many novel findings
for pore formation by the lantibiotic nisin has been presented in of the last few years have uncovered the structure-based activities
Fig. 5A. of lantibiotics, indicating that pore formation is not the major killing
Pore formation by nisin is unique, as compared to that of mechanism of lantibiotics.
vancomycin, teicoplanin, and ramoplanin, in that it subsequently
binds with lipid II, using it as a docking molecule to form a pore that is LIPID-II TARGETING LANTIBIOTIC ACTIVITIES
stable and highly efficient (62). Figure 5B depicts the structure of lipid
II, which portrays the regions involved in the binding of different Bacteria-specific cell wall precursors, e.g., lipid I and lipid II, are
antibiotics. Breukink et al. (4) reported that the presence of lipid II in essential for bacterial cell wall biosynthesis. Many antibiotics bind to
the membrane increases the pore-forming efficiency of nisin 1000- these precursors to interfere with peptidoglycan biosynthesis,
fold as compared to peptides that do not use lipid II. Lipid II-mediated preventing the utilization of these molecules by transpeptidase and
pore formation by nisin is so dramatic that the presence of only two transglycosylase enzymes in building the cross-linked network of the
lipid II molecules per 105 phospholipid molecules greatly enhances bacterial cell wall. Vancomycin (a peptide antibiotic) is an example of a
the release of dyes from vesicles (4, 5). compound that kills bacteria by targeting lipid II and has long been
Nisin forms highly specific pores through its interaction with reliable as an essential antibiotic. Vancomycin binds to the D-Ala-D-
lipid II, and the anion selectivity of nisin in model membrane Ala moiety of lipid II, and nisin binds to the disaccharides-pyropho-
systems disappears upon the addition of lipid II (6). Lipid II changes sphate region of lipid II, so nisin is even effective against vancomycin-

FIG. 5. Pore formation by the lantibiotic nisin using lipid II as a docking molecule. (A) Nisin binds to the cell wall precursor lipid II, using it as a docking molecule. The N-terminus of
nisin binds lipid II, while the C-terminus is inserted into the bacterial membrane, subsequently forming a pore to release molecules and ions. (B) Chemical structure of lipid II. NMR
analysis of the lipid II-nisin complex reveals that the N-terminal region of nisin (residues 1–12) encages the pyrophosphate moiety of lipid II with a hydrogen bond network (43).
482 ASADUZZAMAN AND SONOMOTO J. BIOSCI. BIOENG.,

resistant strains, though both are confined to targeting lipid II (43). It CHANGES IN BACTERIAL MORPHOLOGY BY LANTIBIOTICS
has recently been demonstrated that lipid II is the prime target of
several other classes of natural products, including lantibiotics. A The peptidoglycan of bacteria is a dynamic system, which is the
growing number of lantibiotics have been shown to interfere with prime target of many lantibiotics, including nisin. Hyde et al. (42)
peptidoglycan biosynthesis by binding to lipid II, which act differently showed the effects of nisin on B. subtilis cells, which causes rapid
on lipid II, where different structures of these compounds are used to membrane permeabilization and subsequent changes in length, cross-
explain the sophisticated modes of action directed by the diverse section, shape, and population distributions (Figs. 6 and 7). They
structures of lantibiotics. concluded that the lethal action of nisin is due to the concerted effects
The prototypic type-A(I) lantibiotic nisin is an elongated amphi- of membrane permeabilization, followed by cell wall inhibition and
pathic screw-shaped structure in solution, having a net positive metabolic deregulation of bacterial division. The principal site of
charge. Initially, its bactericidal action was believed to be predomi- action for nisin is located in the region of rapid cell wall growth near
nantly involved in the formation of short-lived pores in bacterial cell the site of septal formation, where the most severe cell wall
membranes (as mentioned before). During the past few years, a malformation occurs (42). Hasper et al. (7) illustrated an action for
unique mechanism of action has been shown to be exerted by nisin, lantibiotics by means of a pyrophosphate-mediated mechanism,
which renders it highly potent against many Gram-positive bacteria through the sequestration of lipid II from sites of bacterial cell wall
at nanomolar concentrations (4, 6). Many ambiguities have been synthesis. These findings are consistent in their explanations invol-
clarified on the modes of action of lantibiotics following the report of ving significant aberrations in cell wall morphogenesis, where
Breukink et al. (4), suggesting that nisin interacts in a highly specific bacterial elongation is rapid. B. subtilis cells exposed to nisin form
manner with lipid II. The dissimilar sensitivities of lipid-II targeting high numbers of double septa near one another and produce a number
lantibiotics to different indicator strains may be due to the presence of multiseptal bacteria.
of different lipid II contents among various microorganisms (e.g., E. We found that the external morphological appearances of B.
coli, 2 × 103 molecules per cell; Micrococcus lysodeikticus, 105 subtilis cells that have been exposed to nukacin ISK-1 are unaltered,
molecules per cell) (65, 66). Many studies have subsequently whereas mersacidin-treated cells showed some changes in the overall
shown that this inhibition is caused by binding to the lipid- morphology. However, cells exposed to nisin show a very different
associated peptidoglycan precursors lipid I and lipid II, with lipid II reaction, which led to a drastic reduction in cell size and abnormal
binding having the more predominant effect (for a review see ref. 67, morphological appearances (Asaduzzaman et al., unpublished data).
68). However, structural information on the interaction of lantibiotics The comparison of these lantibiotic-treated ultra-structures showed
with the cell wall precursor so far has been restricted to lipid II. Nuclear that the cells demonstrated large variations in their internal
magnetic resonance (NMR) data reveal that the pyrophosphate moiety structures, while showing no change in the inner-structure by nukacin
of lipid II interacts with the backbone amides of rings A and B of nisin ISK-1. However, a clear difference was observed in the cross-sections
via six hydrogen bonds (43). Bonev et al. (69) reported that nisin can of nukacin-ISK-1 treated B. subtilis cells, which showed a striking
also bind to bactoprenol pyrophosphate; however, the affinity is reduction in cell wall width after addition of nukacin ISK-1 (Asaduzza-
considerably lower than that for the complete lipid II molecule. This man et al., unpublished observation). The most widely studied type-B
indicates that, for high-affinity binding of nisin, additional interactions lantibiotic, mersacidin, has been reported to cause internal changes in
must take place, presumably between the N-acetylmuramyl moieties, bacterial cells, resulting in the spreading of chromosomes in the
whereas the pentapeptide side chain and the isoprenoid moiety are cytoplasm and ultimately leading to cell lysis (74). In contrast, the
not involved. The inference of the interaction of lantibiotics with lipid well-known type-A(I) lantibiotic nisin is a lytic-bactericidal agent that
I stems mainly from the observation that lipid II biosynthesis is causes multiple aberrations, including leaking of cytoplasmic con-
strongly blocked, but the structural analysis of a lantibiotic-lipid I tents, reduction of cell width, acceleration of cell division, minicell
complex has not yet been reported. The A and B ring system of formation, abnormal morphogenesis of bacterial cells, and eventual
nisin, which has been shown to be responsible for binding with cell death (7, 62).
lipid II, in particular the pyrophosphate moiety, is conserved in
nisin, subtilin, epidermin, gallidermin, and plantaricin C. Bonelli et DISTINCT MODES OF LANTIBIOTIC ACTIONS
al. (49) showed that gallidermin/epidermin has a higher affinity to
lipid II than nisin and suggested that the structural element may be We have already described much of the details of different modes of
lysine at position 4 (isoleucine in nisin), which may provide an the lantibiotic actions that are combined in one molecule. For example,
additional positive charge to enhance binding to the pyrophosphate
moiety.
Mersacidin, actagardin, and cinnamycin are globular type-B
lantibiotics and also bind to lipid II, but have no structural similarity
with nisin and epidermin (Fig. 3). They act by disrupting the
enzyme function of cell wall biosynthesis, by the formation of a
complex with lipid II (48, 70). Specifically, these compounds
prevent the activity of transglycosylases (70). It is important to
note that mersacidin does not form pores upon binding to lipid II;
this is the reason for its moderate MIC values. However, the
compound is very effective in vivo against staphylococcal infections
(71–73), including MRSA and vancomycin-resistant enterococci
(70). In vitro peptidoglycan synthesis assays suggested that
epidermin and nisin accumulate lipid I, indicating that they may FIG. 6. Transmission electron microscopy observations of bacterial cross-section
also inhibit the conversion of lipid I to lipid II (5). The two-peptide projections have been elucidated by Hyde et al. (42). (A) Untreated Bacillus subtilis
lantibiotic laciticn 3147 works at nanomolar concentrations with a cells, in which the cytoplasmic osmotic pressure strengthens the adhesion of the
plasma membrane to the peptidoglycan layer, resulting in circular cross-sections; and
1:1 stoichiometry (LtnA1:LtnA2). The LtnA1 peptide interacts (B) cell wall detachment (indicated by the arrow) from the plasma membrane is visible
specifically with lipid II, which recruits LtnA2 for the inhibition of after nisin exposure, which relieves the osmotic stress by pore formation, leading to an
cell wall biosynthesis and pore formation (46). astral cross-section after contraction of the plasma membrane. Scale bar: 100 nm.
VOL. 107, 2009 MODES OF ACTION OF LANTIBIOTICS 483

FIG. 7. Hyde et al. (42) observed the morphogenesis of Bacillus subtilis cells. (A1 and A2) Normal progression of septal formation in untreated cells; (B–E) some evidence supporting the
suggestion that the bacterial morphogenesis caused by nisin is a result of morphological aberrations during septation: (B) multiseptal divisions, (C) “corkscrew” cell wall
morphologies, (D) disjointed helical septa, and (E) one example of a division “dead end”, which reduces the bacteria to producing many nonviable “minicells”. Scale bar: 200 nm.

the modes of activity of the prototypic lantibiotic nisin have been cell envelope formation is deregulated, leading to aberrant cell
shown to be so sophisticated that its effectiveness as an antibiotic is morphogenesis. They also proposed that this mechanism is distinctly
gradually increasing upon exploration of its structure-based functions. different from the cell wall inhibitory activity of glycopeptides and β-
Early findings on nisin were mainly confined to the observable lactam antibiotics and also from the actions of pore-forming peptide
phenomena of pore formation to release molecules and ions (60, antibiotics. In addition to nisin, many other lantibiotics (e.g.,
75). Up until the last decade, the advances in the molecular gallidermin, subtillin, mersacidin) use lipid II but have distinctive
mechanisms of lantibiotic actions had been very poor. Breukink et al. structure-based activities (5, 49, 70). A notable example of the
(4) were the first to report that peptidoglycan biosynthesis is inhibited molecular modes of action has been elucidated for two-peptide
by nisin, and this led to new insights into the molecular mechanisms of lantibiotics, e.g., laciticin 3147, the well-studied two-component
lantibiotic modes of actions. In a later study, Hsu et al. (43) showed that lantibiotic that works in a sequential manner, where the LtnA1 peptide
the nisin-lipid II complex reveals a novel lipid II-binding motif where interacts specifically with lipid II, then the LtnA2 peptide recognizes
the N-terminal backbone amides of nisin coordinate the pyropho- the LtnA1-lipid II complex for pore formation and peptidoglycan
sphate moiety of lipid II. Furthermore, the sequestration mechanism biosynthesis inhibition (46, 76).
evident from nisin provided insight into how short peptides (e.g.,
gallidermin, epidermin) that may not be capable of spanning the STRUCTURAL VARIANTS TO STUDY MODES OF ACTION
membrane exert their high antibacterial efficacy. Nisin segregates lipid
II into nonphysiological domains in its mode of action (Figs. 8A and B) The mutants and fragments generated by site-directed mutagen-
(7). On the other hand, the glycopeptide antibiotic vancomycin does esis and chemical and enzymatic digestion from many works have
not segregate lipid II from the cell and clearly produces pools of lipid II provided enormous information regarding the modes of action of
in the septum (Fig. 8C). In agreement with the above findings, Hyde et lantibiotics. The introduction of an additional positive charge in nisin
al. (42) demonstrated that, in the presence of nisin, septal formation by the Val32Lys variant has a relatively small effect, whereas a
continues but the bacterial cell displays multiple aberrations, and the negative charge (Val32Glu) results in about a 4-fold decrease in
activity against some indicator strains (6). Epilancin K7 shares a very
similar C-terminus double-ring system with nisin, which does not
show interaction with lipid II (5). This evidence supports the relatively
unimportant role of the C-terminus of these lantibiotics in biological
activity. However, many studies have strongly suggested that the N-
terminus of nisin is essential for binding. For example, a nisin1–12
fragment has no bactericidal activity but shows antagonistic activity
against nisin's bactericidal activity (31), indicating that the fragment
competes with nisin for the binding site. Complete proteolytic
deletion of the D and E rings of nisin leads to a 100-fold decrease
(99% eliminated) in activity (31), whereas chemical disruption of
Dha5, which opens the A ring, results in more than a 500-fold
reduction (less than 0.2%) in antibacterial activity as compared to its
native form (77).
The lipid II variant containing a shorter prenyl tail (3 from 11
isoprene units) can form a complex with nisin, and the length of this
isoprene tail does not affect its pore-forming activity (62). Inter-
FIG. 8. Hasper et al. (7) illustrated an alternative mechanism of nisin's bactericidal
molecular hydrogen bonds between the amides of Dhb2, Ala3, Ile4,
action, which describes the in vivo segregation of lipid II into nonphysiological domains.
(A) Bacillus megaterium cells incubated with 0.5 μg/ml fluorescein-labeled nisin. The Dha5, and Abu8 on nisin and the oxygens of the pyrophosphate group
arrow indicates that the bacterium has already divided. (B) B. subtilis cells incubated of lipid II maintain the pyrophosphate moiety of lipid II within the
with 4 μg/ml fluorescein-labeled nisin. Fluorescence from nisin appears to be clustered cavity. Additionally, MurNAc (N-acetylmuramic acid, a component of
in patches on the membrane. (C) B. megaterium cells after incubation with 2 μg/ml glycan chains) and the first isoprene unit form the binding site for the
labeled vancomycin. The arrows indicate the newly formed division sites or older
recognition of nisin (Fig. 5B). The replacement of Lan in the A ring of
exemplars. (D) B. subtilis cells stained with 4 μg/ml fluorescent vancomycin. The
labeled vancomycin reveals pools of lipid II in the septum and as well as lipid II in helical nisin with MeLan resulted in 50-fold reduced affinity of the peptide to
threads. The insets are Nomarski images. lipid II (6), and it is now well established that chemical opening of the
484 ASADUZZAMAN AND SONOMOTO J. BIOSCI. BIOENG.,

A ring causes a nearly complete loss of activity (77). Further unique modes of action will be revealed, with a new era of amazing
information regarding the binding of nisin and epidermin to both structure-based antibacterial activities.
lipid I and lipid II have been revealed by their NMR structure, in which
both the peptides share a recognition motif (5). Glutamate is RATIONAL AND DE NOVO DESIGN OF LANTIBIOTICS TO
conserved in the A ring of the lacticin 481 subgroup and the B ring REVOLUTIONIZE ANTIBIOTIC REPERTOIRES
of mersacidin, but it is not required for the activity of lacticin 481 (40).
This discovery indicates that, since this residue is critically important The discoveries of the mechanisms involved as individual lanti-
for the A ring of mersacidin (37), lacticin 481 may have a different biotics work as a novel antibacterial, for example, the recent
target or may recognize lipid II in a different manner. discoveries of lipid II as a target for nisin and, in particular, the studies
of the pivotal role played by the pyrophosphate group, have brought
INHIBITION OF SPORE GERMINATION nisin into the forefront as a candidate capable of combating resistant
human infections, as a model case for the design of new antibiotics.
Most studies have mainly focused on the antibacterial activities Furthermore, the insights regarding the segregation of lipid II into
against vegetative cells. Nisin, subtilin, and sublancin inhibit the non-physiological domains (7) elucidate how small lantibiotic pep-
spores' outgrowths from Bacillus and Clostridium species (78, 79). It tides act strongly in vivo by a sequestration mechanism. While it was
has been proposed that this activity is a result of covalent modification previously speculated that NisBTC enzymes had limited specificity, it is
of a target on the spore coat by nucleophilic attack on Dha5, in the case now clear that NisT and NisB have a broad substrate specificity. The
of nisin and subtilin (80). The reactive thiol groups on the exterior of independent functions of NisB, NisC, NisT, and NisP (for a review, ref.
the spores from Bacillus cereus react with compounds such as S- 91) present possibilities for designing new lantibiotics. The design of
nitrosothiols and iodoactetate, and nisin interferes with the modifica- lantibiotics with respect to modification and export may be possible,
tion of these sulfhydryl groups (81), suggesting that the target of nisin based on the findings that NisB-modified peptides can be produced via
for the inhibition of spore germination is provided by these reactive the Sec or Tat system and then cyclized by the in vitro action of NisC
thiol groups (82). However, a covalent mechanism has not yet been (92). The use of lantibiotic synthetases offers much potential for
established. The replacement of Dha5 by Ala via site-directed designing new peptides. For example, Levengood et al. (93) have
mutagenesis of both subtilin (80, 83) and nisin (31) abolished the recently demonstrated the use of LctM in making thioether-containing
inhibition of spore germination, which indicates it as their putative analogs of enkephalin, contryphan, and inhibitors of human tripepti-
site of attack. The above studies clearly suggest that the inhibition of dyl peptidase II and spider venom epimerase. The versatile catalyzing
spore germination is a different lantibiotic activity. Therefore, the capacity of lantibiotic synthetases can thus provide an approach to
inhibition of spore outgrowth is another distinct biological activity of prepare libraries of peptides containing thioether rings and/or
lantibiotics, with a different structure-function relationship. dehydro amino acids to overcome the inefficiency of synthetic
chemistry. In addition, the design of modified peptides combined
FURTHER BIOLOGICAL FUNCTIONS with different lantibiotics has also been explored (94). Furthermore,
the enzymatic actions of lantibiotics' immunity, processing, and
Many lantibiotics have interesting biological activities in addition transportation in combination with its structure-based modes of
to their antibacterial activity. The SapB peptide (Fig. 3) produced by action [for example, (i) the presence of lysines in the hinge region of
Streptomyces coelicolor works as a morphogenic peptide, and the nisin, which increases nisin's activity in killing Gram-negative bacteria
novel lantibiotic sublancin (Fig. 3) exhibits lipid II-independent modes (95), and (ii) the importance of N-terminal lysines in nukacin ISK-1 for
of action, such as the induction of autolysis of staphylococci (79). its membrane binding and activity (41)] may aid in the design of
Cinnamycin (Fig. 3) and duramycin strongly inhibit the phospholipase potential lantibiotics in the future. Moreover, in vitro reconstitutions of
A2 by sequestering its phosphatidylethanolamine (PE) (for multiple lantibiotics are also in progress in order to revolutionize lantibotics for
activities, see review 84), in addition to their bactericidal and enormous applications in the near future.
hemolytic activities (85, 86). Cinnamycin induces transbilayer lipid
movement, seemingly in a PE-dependent fashion (87). APPLICATIONS AND FUTURE OUTLOOK
Nisin and Pep5 also induce autolysis of certain staphylococcal
strains, primarily by breaking down the cell wall at the septa of the The fact that nisin has no known toxicity to humans has placed it in
dividing cells, in addition to their usual modes of action (88, 89). The a unique position of world-wide acceptance as a powerful and safe
positively charged lantibiotics associate with the negatively charged food additive in the control of food spoilage, with widespread
teichoic and lipoteichoic acids, which displace and activate N-acetyl- application as a food preservative in almost 50 countries for over
L-alanine amidase and N-acetylglucosaminidase enzymes (88, 89). 40 years. Nisin has been added to the positive list of food additives by
Though most lantibiotics are reported to use lipid I or lipid II as the European Union (EU) and has also been approved by the Food and
their docking molecule, not all lantibiotics bind to these, as Drug Administration (FDA) (8, 9). Though the proteolytic breakdown
discussed earlier. In most cases, the molecules or mechanisms of nisin in the gastrointestinal tract and its low stability at
involved in the activity have not yet been identified. Pep5 and physiological pH levels limits the initial applications of nisin, nisin
epilancin K7 have specifically been shown to not bind lipid I or lipid and many other lantibiotics are now being used in agricultural,
II (90), but these lantibiotics still show activities against some veterinary, and, more recently, personal care products. Nisin, mutacin,
bacteria that are far greater than those of other pore-forming mersacidin, etc., are in the preclinical stages of medical application
lantibiotics. The high activity of Pep5 at nanomolar concentrations (96). However, the most significant application of lantibiotics may be
against Staphylococcus simulans and S. carnosus signifies that it in the treatment of antibiotic-resistant pathogens. Ryan et al. (97)
employs a different high-affinity receptor or docking molecule for have reviewed the potential biomedical applications of lantibiotics in
its potent biological activity (5, 89). clinical and veterinary therapies. Some notable points are: nisin is
In contrast with lantibiotics, conventional antibiotics do not have effective against bacterial mastitis, oral decay and enterococcal
multiple functions in one molecule and do not possess such unique infections and is effective in peptic ulcer treatment, treatment of
mechanisms of action. Until now, the molecular structure-based enterocolitis, etc.; mersacidin and actagardine show remarkable
functions of only a few lantibiotics have been well clarified. Lantibiotic activity against Staphylococcus aureus including MRSA, bacterial
research is now in an advanced stage, and it is expected that more mastitis, oral decay, acne, etc.; gallidermin and epidermin are effective
VOL. 107, 2009 MODES OF ACTION OF LANTIBIOTICS 485

against acne, eczema, follicultis, and impetigo and can also be used for 16. Sahl, H. G., Jack, R. W., and Bierbaum, G.: Biosynthesis and biological activities of
lantibiotics with unique post-translational modifications, Eur. J. Biochem., 230,
personal care products; mutacin 1140 may prevent dental cavities;
827–853 (1995).
lacticin 3147 is reported to prevent bacterial mastitis, MRSA and 17. Jung, G.: Lantibiotics — ribosomally synthesized biologically active polypeptides
enterococcal infections, prevents oral hygiene, and acne; cinnamycin containing sulfide bridges and α,β-didehydroamino acids, Ang. Chem., Intl. Ed.
may be used for inflamation, viral infection treatment, and blood Engl., 30, 1051–1068 (1991).
pressure regulation; and duramycin and ancovenin can be used for 18. van der Meer, J. R., Rollema, H. S., Siezen, R. J., Beerthuyzen, M. M., Kuipers, O.
P., and de Vos, W. M.: Influence of amino acid substitutions in the nisin leader
inflamation and blood pressure regulation, respectively. Some more peptide on biosynthesis and secretion of nisin by Lactococcus lactis, J. Biol. Chem.,
remarkable applications of nisin have also been reported, which 269, 3555–3562 (1994).
include the inhibition of experimental vascular graft infection caused 19. Xie, L., Miller, L. M., Chatterjee, C., Averin, O., Kelleher, N. L., and van der Donk,
by methicillin-resistant Staphylococcus epidermidis (98), and more W. A.: Lacticin 481: In vitro reconstitution of lantibiotic synthetase activity,
Science, 303, 679–681 (2004).
interestingly, nisin inhibits sperm motility, showing its potential as a
20. Majer, F., Schmid, D. G., Altena, K., Bierbaum, G., and Kupke, T.: The flavoprotein
contraceptive agent (99). As there has been a recent threat of the use MrsD catalyzes the oxidative decarboxylation reaction involved in formation of the
of spores of Bacillus anthracis in bioterrorism, the inhibitory activities peptidoglycan biosynthesis inhibitor mersacidin, J. Bacteriol.,184,1234–1243 (2002).
of lantibiotics, such as subtilin (80, 83) and nisin (31), against spore 21. Schmid, D. G., Majer, F., Kupke, T., and Jung, G.: Electrospray ionization fourier
germination may have interesting and potential future applications. transform ion cyclotron resonance mass spectrometry to reveal the substrate
specificity of the peptidyl-cysteine decarboxylase EpiD, Rapid. Commun. Mass
In the post-genomic era, the combined knowledge of genetics, Spectrom., 16, 1779–1784 (2002).
chemistry, and other approaches can promote new innovations in 22. He, Z., Yuan, C., Zhang, L., and Yousef, A. E.: N-terminal acetylation in
lantibiotics. The systematic research of lantibiotics may further paenibacillin, a novel lantibiotic, FEBS Lett., 582, 2787–2792 (2008).
resolve the existing difficulties and demonstrate potential use in 23. Kuipers, A., de Boef, E., Rink, R., Fekken, S., Kluskens, L. D., Driessen, A. J. M.,
Leenhouts, K., Kuipers, O. P., and Moll, G. N.: NisT, the transporter of the
food agriculture as well as in medical fields.
lantibiotic nisin, can transport fully modified, dehydrated and unmodified
prenisin and fusions of the leader peptide with non-lantibiotic peptides, J. Biol.
ACKNOWLEDGMENTS Chem., 279, 22176–22182 (2004).
24. Havarstein, L. S., Diep, D. B., and Nes, I. F.: A family of bacteriocin ABC
transporters carry out proteolytic processing of their substrates concomitant with
Our work is partly supported by grants from “The Japan Society for export, Mol. Microbiol., 16, 229–240 (1995).
the Promotion of Science (JSPS)”. 25. Heidrich, C., Pag, U., Josten, M., Metzger, J., Jack, R. W., Bierbaum, G., Jung, G.,
and Sahl, H. G.: Isolation, characterization, and heterologous expression of the
novel lantibiotic epicidin 280 and analysis of its biosynthetic gene cluster, Appl.
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