The crystal structure complex with platensimycin employed a C163Q mutant, which gave a 50-fold increase in apparent binding. The Gln163 residue lies adjacent to the carboxylate of platensimycin but makes no specific hydrogen bond. The close proximity of the carboxylate of platensimycin (presumed to be an anion) to the anionic thiol of Cys163 in the wild type enzyme may suggest the reason behind the increase in binding of the C163Q mutant. The second set of residues worth considering comprises His303 and His340, which play a role in the decarboxylation mechanism of the malonyl moiety. In particular, His303 activates a structured water to attack the carboxylate of the incoming malonyl-ACP. The crystal structure of FabF also demonstrates that His340 forms a hydrogen bond between the amide nitrogen of Leu342 and the N-delta- atom of the imidazole ring meaning that the lone pair must reside on this atom. In the platensimycin crystal structure the structured water adjacent to His303 is no longer present which may suggest an alternative electronic state for this residue. A strong possibility exists that His303 would present itself as a cation capable of forming an ionic interaction with the benzoic acid group of platensimycin.