Proposed arrangement of proteins forming a bacterial type II polyketide synthase.

Aklanonic acid is synthesized by a type II polyketide synthase (PKS) composed of eight protein subunits. The network of protein interactions within this complex was investigated using a yeast two-hybrid system, by coaffinity chromatography and by two different computer-aided protein docking simulations. Results suggest that the ketosynthase (KS) alpha and beta subunits interact with each other, and that the KSalpha subunit also probably interacts with a malonyl-CoA:ACP acyltransferase (DpsD), forming a putative minimal synthase. We speculate that DpsD may physically inhibit the priming reaction, allowing the choice of propionate rather than acetate as the starter unit. We also suggest a structural role for the cyclase (DpsY) in maintaining the overall structural integrity of the complex.