Precursor-directed biosynthesis

Keywords Chalcone synthase superfamily enzyme, Engineered biosynthesis, Precursor-directed biosynthesis, Structure-based engineering, Type III polyketide synthase... 

A number of mitomycin analogues have been prepared by precursor-directed biosynthesis [104]. A range of amines were fed to S. caespitosus, and novel derivatives of mitomycin C (type I analogues) and mitomycin B (type II analogues) were identified and in some cases (42-46 and 52-56 Scheme 11.4) isolated and characterized. Antibiotic and antitumor activities were comparable to those of mitomycin C, with the type I analogues more active than the type II analogues. 

Jacobsen, J.R., Keatinge-Clay, A.T., Cane, D.E. and Khosla, C. (1998) Precursor-directed biosynthesis of 12-ethyl erythromycin. Bioorganic and Medicinal Chemistry, 6, 1171. 

Ward, S.L., Desai, R.P., Hu, Z. et al. (2007) Precursor-directed biosynthesis of 6-deoxyerythronolide B analogues is improved by removal of the initial catalytic sites of the polyketide synthase. Journal of Industrial Microbiology and Biotechnology, 34, 9-15. 

Thiericke, R. and Rohr, J. (1993) Biological variation of microbial metabolites by precursor-directed biosynthesis. Natural Product Reports, 10 (3), 265-289. 

Engineered Biosynthesis of Plant Polyketides Structure-Based and Precursor-Directed Approach... 

Bu Lock et al. had shown initially [24] that supplementation of S. avermitilis fermentations with a range of fatty acids resulted in their uptake and incorporation to generate novel avermectins modified at the C25 side chain of the molecule. This approach, described as precursor-directed biosynthesis, has been employed to produce many new antibiotics [25], but the co-expression of the parent molecule interferes with the detection and isolation of the novel analogs. To circumvent these difficulties, the elegant technique of mutational biosynthesis [26] or mutasynthesis [27,28] was developed. In this approach, a mutant of an organism, deficient in the production of an essential precursor for the secondary metabolite of choice, is isolated, and precursor-directed biosynthesis is then employed to generate only the novel analogs. 

Figure 9 Precursor-directed biosynthesis. A block in the 6-dEB pathway was created by a Cys— Ala mutation in the active site of the KS of module 1. Feeding diketides with different a and j substitutions resulted in the 6-dEB analogs in which the starter unit or first extender unit was modified. The stereochemistry of an unsaturated triketide dictated whether it was incorporated into module 2 or 3, leading to either a 14-membered or 16-membered macrolactone. See Sec. VI.C for details.

JR Jacobsen, CR Hutchinson, DE Cane, C Khosla. Precursor directed biosynthesis of novel erythromycin analogs by an engineered polyketide synthase. Science 277 367-369, 1997. 

A third approach is precursor-directed biosynthesis in which altered starter unit functionality is introduced through the incorporation of a synthetic non-natural diketide intermediate into a polyketide product in vivo. This strategy was first... 

Figure 21 Precursor-directed biosynthesis using bimodular PKSs. Both DEBS 1-TE and DEBS 1+TE (KS,°) were shown to process a range of diketide analogs to the corresponding triketide lactones in vitro.

KJ Weissman, M By croft, AL Cutter, U Hanefeld, EJ Frost, MC Timoney, R Harris, S Handa, M Roddis, J Staunton, PF Leadlay. Evaluating precursor-directed biosynthesis towards novel erythromycins through in vitro studies on a bimodular polyketide synthase. Chem Biol 5 743-754, 1998. 

Tailoring modification, known as metabolic engineering, biotransformation or precursor-directed biosynthesis, involving the feeding of building blocks which are subsequently modified by a specific enzyme involved in the biosynthesis of a structurally related drug (752) (Fig. IF). 

Mutasynthesis, also called mutational biosynthesis, involving precursor-directed biosynthesis using a mutant strain blocked in a crucial biosynthetic step, which then incorporates the alternative substrate to produce an analog of the wild-type compound 119,122) (Fig. lA, F). 

Primer Unit Engineering and Precursor-Directed Biosynthesis... 

Using precursor-directed biosynthesis, Boddy et a/. were able to effectively reconstitute epothilone biosynthesis in E. coli. A pentaketide NAC thioester intermediate... 

Scheme 1 Examples of precursor-directed biosynthesis (PDB) of fungal metabolite analogues...

There are many examples of polyketide metabolites where the common acetate starter unit is replaced by other groups, and a general discussion of these is outside the scope of this review. Numerous studies have been carried out on the use of analogues of the normal biosynthetic precursors to produce novel structures. This type of precursor-directed biosynthesis has been the subject of a recent comprehensive review [60]. 

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