Cloning, expression, and purification of intact polyketide synthase modules.

Polyketides are a structurally and functionally diverse family of bioactive natural products that have proven to be a rich source of pharmaceutical and agrochemical lead compounds. Many polyketides are biosynthesized by large multifunctional megaenzymes termed type I modular polyketide synthases (PKSs). These systems possess a distinctive assembly line-like architecture, comprising a series of linearly arranged, multidomain extension modules, housed in sequence within giant polypeptide chains. Due to their inherently modular structures, PKSs represent attractive targets for reengineering, enabling access to functionally optimized "nonnatural" natural products. In this chapter we describe methods for the molecular cloning, recombinant over-expression, and purification of intact PKS modules and multimodular PKS polypeptides. The usefulness of these methods is demonstrated by applying them to the study of the abyssomicin C PKS, a >1MDa multimodular synthase responsible for the biosynthesis of a polyketide antimicrobial lead compound.