Aquastatin A, a New Inhibitor of Enoyl-Acyl Carrier Protein Reductase from Sporothrix sp FN611

Bacterial enoyl-acyl carrier protein (ACP) reductase has been confirmed as a novel target for antibacterial drug development. In this study, we determined that a fungal metabolite from Sporothrix sp. FN611 potently inhibited the enoyl-ACP reductase (FabI) of Staphylococcus aureus. Its structure identified the metabolite as aquastatin A by the MS and NAIR data. Aquastatin A inhibited S. aureus FabI with an IC50 of 3.2 mu M. It also prevented the growth of S. aureus and methicillin-resistant Staphylococcus aureus (MRSA) with minimum inhibitory concentration of 16-32 mu g/ml. Aquastatin A also exerted an inhibitory effect against the FabK isoform, an enoyl-ACP reductase of Streptococcus pneumoniae, with an IC50 of 9.2 mu M. The degalactosylation of aquastatin A did not affect the FabI and FabK-inhibitory or antibacterial activities, thereby suggesting that the sugar moiety within its molecular structure was not involved in these activities. The inhibitory effects of aquastatin A and its degalactosylated derivative on enoyl-ACP reductases and bacterial viability are reported for the first time in this study; these effects point to the potential that aquastatin A may be developed into a new broad-spectrum antibacterial and anti-MRSA agent.