Crystal structure and fluorescence studies reveal the role of helical dimeric interface of staphylococcal FabG1 in positive cooperativity for NADPH

Crystal structure of Staphylococcal β‐ketoacyl‐ACP reductase 1 (SaFabG1) complexed with NADPH is determined at 2.5 Å resolution. The enzyme is essential in FAS‐II pathway and utilizes NADPH to reduce β‐ketoacyl‐ACP to (S)‐β‐hydroxyacyl‐ACP. Unlike the tetrameric FabGs, dimeric SaFabG1 shows positive homotropic cooperativity towards NADPH. Analysis of FabG:NADPH binary crystal structure endorses that NADPH interacts directly with the helices α4 and α5 those are present on a dimerization interface. A steady shift in tryptophan (of α4 helix) emission peak upon steady increment of NADPH concentration reveals that the dimeric interface is formed by α4‐α4′ and α5‐α5′ helices. This dimeric interface imparts positive homotropic cooperativity towards NADPH. PEG, a substrate mimicking molecule is also found near the active site of the enzyme. Proteins 2012; © 2011 Wiley Periodicals, Inc.