Mapping the active site ofEscherichia colimalonyl-CoA–acyl carrier protein transacylase (FabD) by protein crystallography

Malonyl-CoA-acyl carrier protein transacylase (FabD; EC 2.3.1.39) is a key enzyme in the fatty-acid biosynthesis pathway of bacteria, catalyzing the transfer of a malonyl moiety from malonyl-CoA to holo acyl carrier protein (ACP), generating malonyl-ACP and free CoASH. Malonyl-ACP, which is the product of this reaction, is the key building block for de novo fatty-acid biosynthesis. Various binary complex structures of the Escherichia coli enzyme are presented, including that of the natural substrate malonyl-CoA, indicating the functional role of the highly conserved amino acids Gln11, Ser92, Arg117 and His201 and the stabilizing function of the preformed oxyanion hole during the enzymatic reaction. Based on the presented structural data, a possible new catalytic enzyme mechanism is discussed. The data obtained could be used in aiding the process of rational inhibitor design.