Modular polyketide synthesis

KEH Wiesmann, J Cortes, MJB Brown, AL Cutter, J Staunton, PF Leadlay. Polyketide synthesis in vitro on a modular polyketide synthase. Chem Biol 2 583-589, 1995. 

NL Pohl, RS Gokhale, DE Cane, C Khosla. Synthesis and incorporation of an N-acetyl cysteamine analog of methylmalonyl-CoA by a modular polyketide synthase. J Am Chem Soc 120 11206-11207, 1998. 

The modular design of PKS and NRPS renders them convenient for protein engineering to generate hybrid enzymes that can synthesize a range of natural and unnatural metabolites. By independently manipulating what Cane et al. [143] call the four degrees of freedom in polyketide synthesis variation of chain length, choice of ACP... 

Pieper R, Luo C, Cane DE, Khosla C. Remarkably broad substrate specihcity of a modular polyketide synthase in a cell-free system. J Am Chem Soc 1995 117 11373-11374. Wiesmann KEH. Coites J, Brown MJB, Cutter AL, Staunton J. Leadlay PF. Polyketide synthesis in vitro on a modular polyketide synthase. Chem Biol 1995 2 583-589. 

Modular Polyketide Synthases (Type I). In contrast to iterative PKSs, modular PKSs consist of one or more large proteins composed of synthase units called modules (Donadio et al. 1991). Each module performs an elongation step of the synthesis of the polyketide chain. In all the modules are present the enzymes necessary for the condensation of an extension unit of the growing chain acylketosynthase (KS), acyltransferase (AT), and acyl carrier protein (ACP). In some modules, also present may be some or all of the enzymes devoted in fatty acid synthesis to the stepwise reduction of keto groups ketoreductase... 

Donadio S, Staver MJ, McAlpine JB, Swanson SJ, Katz L (1991) Modular organization of genes required for complex polyketide biosynthesis. Science 252 675-679 Donadio S, McAlpine JB, Sheldon PA, Jackson MA, Katz L (1993) An erythromycin analog produced by reprogramming of polyketide synthesis. Proc Natl... 

Experiments in vitro with modular PKSs are considerably more straightforward than those with aromatic synthases. Whereas synthesis of aromatic polyketides requires the expression and purification of at minimum three activities, and as many as seven, a single multienzyme from a modular PKS can be competent for synthesis. Additionally, the design rules for the modular PKSs are considerably simpler, as there is a direct correlation between the number and nature of activities present and the resulting structure of the polyketide product. 

Three categories of synthetases are distinguished, based on their substrate specificity and mode of product synthesis. The two known types of polyketide synthetases (PKSs) (Type I and II) utilize acyl-coenzyme A (CoA) monomers while nonribosomal peptide synthetases (NRPSs) use amino acids and their analogs as substrates. Type I PKS and NRPS oligomerize these building blocks by a modular assembly-line arrangement while type II PKS iteratively assembles monomeric units. 

Many enzymes are involved in the synthesis of secondary metabolites. The modular biosynthetic enzymes polyketide synthase (PKS) and nonribosomal peptide synthetase (NRPS) are responsible for the generation of a multitude of structurally diverse and biologically important small-molecule natural products. A complex carbon structure is assembled sequentially from simple carbon building blocks (acyl-CoA and amino acids). The elongation of each carbon unit is catalyzed by... 

Six orfs (fscA fscF) encoding typical multifunctional type I PKS subunits, with exactly 21 PKS modules, were found, in agreement with the 21 condensation steps required for the synthesis of the carbon skeleton of FR-008 polyketide. The modular organization of candicidin/FR-008 PKS genes fscA-fscF is shown in Figure 7.53. 

Bode JW, Fraefel N, Muri D, Carreira EM. A general solution to the modular synthesis of polyketide building blocks by Kanemasa hydroxy-directed nitrile oxide cycloadditions. Angew. Chem. Int. Ed. 2001 40 2082-2085. 

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