Zagazig University Faculty of Pharmacy
Plant Biotechnology-Pharmacognosy
Department
Research Project
Biotransformation Pathways
Presented
By:
Student Name: Menna Osama Mahmoud Elbayaa
Academic Year: 4th
Seat Number: 8785
Student ID: 051500613
Student Code: 20612015202293
Phone Number:01149850965
Under the Supervision of:
Prof. Dr. Rehab Hamed
Table of Contents
Introduction ................................................................................................................3
Biotransformation Pathways ......................................................................................4
1. Shikimate Pathway ..............................................................................................4
2. Mevalonate Pathway for supply of IPP and DMAPP .........................................5
3. Deoxyxylulose phosphate pathway .....................................................................7
4. Polyketide pathway ..............................................................................................8
Biotransformation of flavonoids ............................................................................9
Biotransformation of Phloroglucinol, the Simplest Polyketide Derived Aromatic
Compound ............................................................................................................10
5. Phenylpropanoid Pathway .................................................................................11
References ................................................................................................................13
Introduction
Biotransformation is an area of biotechnology constantly gaining considerable
attention. Biotransformation is the plant cell culture’s ability to catalyze the
conversion of readily available and inexpensive precursors into a much more.
valuable product as shown in (Table 1).
Biotransformation Pathways
1. Shikimate Pathway
The shikimate pathway (Figure 1) takes part in the synthesis of acridone and indole
alkaloids via tryptophan or anthranilic acid. Tyrosine is a precursor in a variety of
compounds as in the protoberberine type, morphinamine, benzyleisoquinoline, and
benzophenanthridine alkaloids; the intermediate being reticuline. Pyridine alkaloids
as nicotine and tropane alkaloids like cocaine are derived from ornithine, where the
polyamine putrescine is a common precursor however, the pathway deviate before
the formation of tropolone. The amino acid phenylalanine is required in addition to
ornithine for the synthesis of the molecule littorine backbone, for a second class of
tropane alkaloids, which is an intermediate to the path to scopolamine and
hyoscyamine. Putrescine is converted to homospermidine, which in tur is
metabolized forming retronecine which is the pyrrolizidine alkaloids precursor. The
reaction that converts homospermidine is catalyzed by the enzyme homospermidine
synthase which is the first specific enzyme of this pathway [1].
Figure 1 Overview on Biotransformation Pathway of Selected Alkaloids
2. Mevalonate Pathway for supply of IPP and DMAPP
Although many important terpenoids and terpenoid derivative synthesized via plant
cell culture originate from DMAPP and IPP produced trough the non-Mevalonate
pathway, recent studies showed cross linking between the MEP and MVA pathways
suggesting that MVA pathway engineering could be of use in formation of isopentyl
pyrophosphate (IPP), controlling plastidal terpenoid biotransformation. Although
both reactions can happen simultaneously in a plant, while some organisms only use
one pathway. When coupled to the ER, the oxidation step is catalyzed by CYP450
dependent monooxygenases. As mentioned before the MVA and MEP pathways
interact with each other and both are essential in IPP and DMAP formation which
are used in the biotransformation or higher molecular weight terpenes; the reaction
being catalyzed by prenyltranseferases. The essential enzymes for the MVA
pathway are hydrooxymethylglutaryl-CoA reductase and synthase catalyzing the
mevalonic acid formation. HMG-CoA reductase is strictly regulated in plant
systems, and elicitor-induced HMG CoA reductase genes have been characterized
and cloned in numerous plant systems. The last step for the pathway is catalyzed
terpene synthase which are encoded by multigene families and thus able to
synthesize longer chain terpenes from diphosphate molecules [4].
Figure 2 MEP and MVA biotransformation pathways for the biothenthesis of IPP and DMAPP
3. Deoxyxylulose phosphate pathway
Deoxyxylulose phosphate pathway is widely distributed in plants. Isotope
incorporation studies using plant cell culture and plat tissues showed the formation
of IPP and DMAPP from exogenous 1-deoxyxylulose. Crosstalk between
mevalonate and deoxyxylulose phosphate pathway is observed in plants. In higher
plants the mevalonate pathway operates in the mitochondria and cytoplasm;
sesquiterpenes, sterols and ubiquinones are biosynthesized predominantly by
mevalonate. The compartmental separation between the two different IPP
biotransformation pathway is not absolute because at least one metabolite can be
exchanged between them. The extent of the mentioned crosslink depends on the
species and additionally on the presence and concentration of exogenous precursors.
Higher values have been found in plants cell cultures in the presence of 1-
deoxyxylulose or mevalonate.
Figure 3 Deoxyxylulose phosphate pathway
4. Polyketide pathway
Polyketide natural products possess different skeletal patterns and occur in plants,
fungi, and soil bacteria. They exhibit important medicinal antibiotics, antiparasitic,
anticancer, immunosuppressive, and antifungal activities. They are also used as food
nutraceuticals and ingredients [3]. The initial carbon chain of a polyketide is formed
by a series of intermolecular Claisen condensation of malonyl coenzyme A which is
an elongation of the chain by C2 unit. The latter is formed from acetyl coenzyme A
by carboxylation. The majority of polyketide natural products are produced by three
broad classes of polyketide synthases sharing a similar mechanistic approach, the
sequential decarboxylative condensation. The three classes of PKSs are,
• multienzyme type 1,
• iterative type II PKSs, and
• the homodimeric type III
which are involved in the formation of a large range of aromatic compounds like
flavonoids and chalcones (Figure 4).
Figure 4 Biotransformation of orsellinic acid
Biotransformation of flavonoids
The gross C6–C3–C6 carbon content of flavonoids comes from (a) 4-coumaroyl
coenzyme A, a product of shikimic acid pathway (Figure 1), which provides:
• ring B and the C3 part of the middle heterocyclic ring (ring C),
• and (b) three molecules of malonyl coenzyme A (precursor of ring A), a
biotransformation entity in polyketide formation.
In the biotransformation pathway of flavonoids, the first C6–C3–C6 compound is a
chalcone which is catalyzed by chalcone synthase from which the middle six-
membered heterocyclic ring is generated by intramolecular Michael addition
(Figure 5).
Figure 5 Biotransformation Pathway of Flavonoids
Biotransformation of Phloroglucinol, the Simplest Polyketide Derived
Aromatic Compound
For the Biotransformation of phloroglucinol and dehydroacetic acid, three molecules
of malonyl coenzyme are required which are as follows (Figure 6):
• Decarboxylation of the COOH group of the priming malonyl coenzyme would
lead to the formation of 3,5-diketohexanoate
• An intermediate for triacetic acid lactone while the retention of the said
COOH group would form 3,5-diketoheptane dionate
• An intermediate for phloroglucinol. [3]
Figure 6 Biotransformation of acetylphloroglucinol via phloroglucinol
5. Phenylpropanoid Pathway
The phenylpropanoid pathway is a rich source of metabolites in plants, being
required for the biotransformation of lignin, and serving as a starting point for many
other important compounds production, such as the coumarins, flavonoids, and
lignans. In spite of the fact that the phenylpropanoids and phenylpropanoids
derivatives are classified sometimes as secondary metabolites, their relevance to
plant survival has been made obvious via the study of Arabidopsis and other species
of plant [2]. Phenylpropanoids are a different group of compounds originally from
the carbon skeleton of phenylalanine involved in plant defense, structural support,
and survival phenylalanine is an end product of the shikimate pathway, which also
gives rise to the aromatic amino acid tryptophan and tyrosine. From phenylalanine,
lignin biotransformation proceeds via a chain of side-chain alterations and ring
hydroxylations and O-methylations to produce the lignin monomers. The pathway
also gives rise to a host of other small molecules such as the lignans, flavonoids,
coumarins, and hydroxycinnamic acid conjugates [5]. The phenylpropanoid
pathway begins with three reactions leading to the synthesis of 4-coumaroyl CoA.
The initial three steps of the pathway catalyzed by cinnamate 4-hydroxylase, PAL,
and 4-coumaroyl CoA-Ligase are mandatory and deliver the basis for all following
branches and subsequent metabolites. Next steps downstream of PAL, leading to
phenylpropanoid monomers except cinnamate 4-hydroxylase (Figure 7).
Figure 7 Phenylpropanoid Pathway
References
1. Eisenreich, W., Rohdich, F., & Bacher, A. (2001). Deoxyxylulose phosphate
pathway to terpenoids. Trends In Plant Science, 6(2), 78-84. doi:
10.1016/s1360-1385(00)01812-4
2. Fraser, C., & Chapple, C. (2011). The Phenylpropanoid Pathway in
Arabidopsis. The Arabidopsis Book, 9, e0152. https://doi.org/10.1199/tab.0152
3. Talapatra, S., & Talapatra, B. (2014). Polyketide Pathway. Biosynthesis of
Diverse Classes of Aromatic Compounds. Chemistry Of Plant Natural
Products, 679-715. https://doi.org/10.1007/978-3-642-45410-3_14
4. Vickery, M., & Vickery, B. (2008). The Acetate-Mevalonate
Pathway. Secondary Plant Metabolism, 112-156. https://doi.org/10.1007/978-1-
349-86109-5_5
5. Vogt, T. (2010). Phenylpropanoid Biosynthesis. Molecular Plant, 3(1), 2-20.
https://doi.org/10.1093/mp/ssp106
