Fig. 3: Structure of complex B with a single ACP = KS crosslink.
From: Visualizing acyl carrier protein interactions within a crosslinked type I polyketide synthase
a Map of one ACP crosslinked at KS’ within the condensation compartment at 3.2 Å, with a contour level of 0.12. Colored circles represent regions of expansion in (b–e). Panel (f) further distinguishes the KS and KS’. b Crosslinking of ACP and KS traps PPIs between ACP and KS. A single hydrogen bond between Glu79 and Arg2045 mediates the ACP interaction with KS. c More extensive residue interactions are seen between ACP and AT. d The KS gating network (gating loops 1 and 2) residing at the entrance of the KS substrate binding tunnel demonstrates the inter-loop interactions (Asn272, Asp274, and Asn421) and its interactions with the PPant arm of 1. This gate is visualized in both KSs in complex A. e Crosslinker 1 links ACP to KS by trapping Cys177 (Fig. 1b), highlighting active site residues in the substrate loading and reloading states (Fig. 1a). f Demonstration of the deep KS binding tunnel formed by the KS • KS’ dimerization interface. In complex B, one ACP is crosslinked at KS, while KS is shunted by 1 without ACP.
