Fig. 5: Structural insight into MAS conformationally-guided processivity.
From: Visualizing acyl carrier protein interactions within a crosslinked type I polyketide synthase
Following KS (at KS and KS’), ACP•KS substrate reloading occurs through transacylation from ACP. Next, ACP accepts a methylmalonate monomer from AT. ACP shuttles the extension unit to its partner KS to induce condensation. Complex B informs this step. MAS flexibility enables in plane tilting and out-of-plane twisting. During this process, ACP is distal to the condensation compartment, therefore, interactions with the modifying compartment are favored, and the ACP binds sequentially to KR, DH, and ER. Dehydration processing is exemplified in complexes C and D, where complex D is trapped through crosslinking of ACPs with DH (chamber 1) and KS (chamber 2), respectively, showing this conformational movement. A full iteration is completed through substrate reloading. After 4 iterations, PapA5 transfers the mature mycocerosates to phthiocerol, forming phthiocerol dimycocerosate (PDIM).
