Biosynthesis manipulation

Figure 4.22 Combinatorial biosynthesis manipulation of the aromatic polyketide pathway.

Figure 10.46 Combinatorial biosynthesis manipulation of the ring size and the stereochemical transformations of DEBS modules to produce analogues 10.77 and 10.78.

Figure 10.47 Combinatorial biosynthesis manipulation and substitution of whole DEBS modules to produce 10.70,10.71 and 10.79.

In this chapter, by using the examples of -lactams we have briefly examined how microbial cultures may be used to produce sufficient antibiotics to meet market demands. We have also explained how enzymes (or cells) may be used to biotransform, and thereby diversify, antibiotics. By outlining the history of penicillin production, we explained how analysis and manipulation of culture regimes may be used to enhance the yields of antibiotics (and other secondary products). These studies led to die concept of directed biosynthesis by precursor feeding. 

Since carotenoids are derived for the central isoprenoid pathway (Fig. 13.3), the regulation of their formation must involve a co-ordinated flux of isoprenoid imits into this branch of the pathway as well as into others such as the biosynthesis of sterols, gibberellins, phytol and terpenoid quinones. An imderstanding of the complexities of regulation of the pathway is necessary in order to target the regulatory steps for genetic manipulation. 

BRAMLEY p M (1997) The regulation and genetic manipulation of carotenoid biosynthesis in tomato fruit , PureAppl Chem, 69, 2159-62. 

Niyogi, K.K., Safety valves for photosynthesis, Curr. Opin. Plant Biol. 3, 455, 2000. Pogson, B.J. and Rissler, H.M., Genetic manipulation of carotenoid biosynthesis and photoprotection, Philos. Trans. R. Soc. Lond B 355, 1395, 2000. 

Iuchi, S., M. Kobayashi et al. (2001). Regulation of drought tolerance by gene manipulation of 9-cis-epoxycarotenoid dioxygenase, a key enzyme in abscisic acid biosynthesis in Arabidopsis. Plant J. 27(4) 325-333. 

Taylor, I. B., T. Sonneveld et al. (2005). Regulation and manipulation of the biosynthesis of abscisic acid, including the supply of xanthophyll precursors. J. Plant Growth Reg. 24(4) 253-273. 

Walter, M. H., D. S. Flo et al. (2007). Apocarotenoid biosynthesis in arbuscular mycorrhizal roots Contributions from methylerythritol phosphate pathway isogenes and tools for its manipulation. 

Bushell, M.E., Kirk, S., Zhao, H.-J. and Avignone-Rossa, C.A. (2006) Manipulation of the physiology of clavulanic acid biosynthesis with the aid of metabolic flux analysis. Enzyme and Microbial Technology, 39, 149-157. 

The above observations suggested that hexoses arise in Nature by reaction of glycerose with dihydroxyacetone. A vast amount of practical information has been derived from investigation of plant- and muscle-extracts, two dissimilar systems that show many similarities in their biosynthetic manipulations. There is a close parallelism in the sequence of intermediates involved in the processes wherein D-glucose is converted to ethanol and carbon dioxide by yeasts, and to lactic acid by muscle during contraction. The importance of these schemes lies in their reversibility, which provides a means of biosynthesis from small molecules. 

Plant metabolism can be separated into primary pathways that are found in all cells and deal with manipulating a uniform group of basic compounds, and secondary pathways that occur in specialized cells and produce a wide variety of unique compounds. The primary pathways deal with the metabolism of carbohydrates, lipids, proteins, and nucleic acids and act through the many-step reactions of glycolysis, the tricarboxylic acid cycle, the pentose phosphate shunt, and lipid, protein, and nucleic acid biosynthesis. In contrast, the secondary metabolites (e.g., terpenes, alkaloids, phenylpropanoids, lignin, flavonoids, coumarins, and related compounds) are produced by the shikimic, malonic, and mevalonic acid pathways, and the methylerythritol phosphate pathway (Fig. 3.1). This chapter concentrates on the synthesis and metabolism of phenolic compounds and on how the activities of these pathways and the compounds produced affect product quality. 

In order to synthesize biologically relevant phosphonylimidazole 73, bromoimidazole 72 was derived from radical-initiated bromination of methyl l-p-methoxybenzyl-2-thiomethyl-5-imidazolylcarboxylate (71) [56]. The thiomethyl group served to block the C(2) position, which would otherwise undergo preferential halogenation under these conditions. As expected, a variety of Arbusov-Michaelis reaction conditions failed even under forcing conditions. On the other hand, Pd-catalyzed phosphorylation of 72 with diethyl phosphite led to methyl-4-diethylphosphonyl-l-p-methoxybenzyl-2-thiomethyl-5-imidazolylcarboxylate (73). After further manipulations, the desired phosphonic acid-linked aminoimidazoles, which resembled intermediates formed during purine biosynthesis, were accessed. 

The study of individual NRPS domain structures provides important information regarding the specificity and enzymology of individual steps in NRP biosynthesis. However, structural analysis of larger NRPS constructs is necessary to gain insight into aspects related to domain/domain interactions and the overall structure of the synthetase machinery. This information is particularly important for understanding the details of substrate trafficking and will assist efforts toward the rational manipulation of NRPSs. 

Targeting Volatile Terpene Biosynthesis for Manipulating Indirect Plant Defenses... 

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