Fatty acid biosynthesis type II (FAS II) pathway has been studied as target to develop novel antibacterial drugs. β-Ketoacyl ACP synthases (KAS) are critical enzymes in FAS II, where they elongate acyl chains by condensing the acyl primer carried by coenzyme A or acyl carrier protein (ACP) with a malonyl-ACP. There are two KAS enzymes in Staphylococcus aureus (S. aureus), one of the most prevailing gram-positive pathogens. saFabH, also referred as KAS III, catalyzes the initial condensing step of the FAS II pathway, and saFabF, or KAS II, catalyzed the condensing reactions in the following elongation cycles. Natural products, such as thiolactomycin and platensimycin, have been studied to seek for potential antibiotics targeting these KAS enzymes, and some highly potent and selective inhibitors have been discovered. Here, the binding of thiolactomycin-based compounds to saFabF was tested. All of these compounds were identified as rapid reversible inhibitors against the enzyme, and one of them showed relatively high binding affinity. Besides, the inhibition study was extended to another natural product, platensimycin, which has been determined as a selective inhibitor against FabB/FabF and is believed inactive against FabH. Howere, 3 FabH mutants, T37I, F209S, G297V, were found in platensimycin-resistant S. aureus. One hypothesis is that these FabH mutants may be able to play the role of FabF. Natural substrates of FabF, lauroyl-ACP and malonyl-ACP have been synthesized and the activity of FabH variants with these substrates were tested. The assay demonstrated that all these mutants were as active as the wild type with their natural substrates. Moreover, T37I mutant showed activity with FabF substrates and F209S mutant showed activity with lauroyl-CoA. The activity of G297V still needs to be confirmed. These preliminary results indicate that the single mutations are able to shift the substrate specificity of saFabH and help the bacteria to survive under drug selection.

Inhibiting β-ketoacyl acyl carrier protein synthases in Staphylococcus aureus

249th National Meeting (2015)

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