Inhibition of beta-ketoacyl-acyl carrier protein syntheses by thiolactomycin and cerulenin - Structure and mechanism

The beta -ketoacyl-acyl carrier protein (ACP) synthases are key regulators of type II fatty acid synthesis and are the targets for two natural product s, thiolactomycin (TLM) and cerulenin. The high resolution structures of th e FabB-TLM and FabB-cerulenin binary complexes were determined. TLM mimics malonyl-ACP in the FabB active site. It forms strong hydrogen bond interact ions with the two catalytic histidines, and the unsaturated alkyl side chai n interaction with a small hydrophobic pocket is stabilized by pi stacking interactions. Cerulenin binding mimics the condensation transition state. T he subtle differences between the FabB-cerulenin and FabF-cerulenin (Moche, M., Schneider, G., Edwards, P., Dehesh, K., and Lindqvist, Y. (1999) J. Bi ol. Chem. 244, 6031-6034) structures explain the differences in the sensiti vity of the two enzymes to the antibiotic and may reflect the distinct subs trate specificities that differentiate the two enzymes. The FabB[H333N] pro tein was prepared to convert the FabB His-His Cys active site triad into th e FabH His-Asn-Cys configuration to test the importance of the two His resi dues in TLM and cerulenin binding. FabB[H333N] was significantly more resis tant to both antibiotics than FabB and had an affinity for TLM an order of magnitude less than the wild-type enzyme, illustrating that the two-histidi ne active site architecture is critical to protein-antibiotic interaction. These data provide a structural framework for understanding antibiotic sens itivity within this group of enzymes.