Figure 3.

Catalytic cycle of DEBS module 2. Domains are colored as in Figure 1. The cycle includes four reactions: translocation of the growing polyketide chain (I) into and (IV) out of the module, (II) transacylation of an extender unit from methylmalonyl-CoA to its ACP domain, and (III) chain elongation via decarboxylative C–C bond formation. Module 2 also reduces the β-keto thioester product of chain elongation; this reaction is lumped into step III.