Fig. 1.

Modular organization of the 6-deoxyerythronolide B synthase. Organized into three homodimeric polypeptides (DEBS1–3), DEBS consists of six modules, each containing a unique set of covalently linked domains. Noncovalent interactions localized to the termini of each polypeptide (matching black tabs) play an important role in chain translocation between modules 2 and 3 and modules 4 and 5. Together, the six modules of this assembly line utilize one propionyl-CoA-derived primer and six methylmalonyl-CoA-derived extender units to synthesize 6-deoxyerythronolide B (6-dEB). DH, dehydratase; ER, enoylreductase; TE, thioesterase; LDD, loading didomain. KR° in module 3 is inactive. The phosphopantetheine prosthetic group of the ACP is shown as a wavy line.