Malonyl-CoA-acyl carrier protein transacylase is a key enzyme in the fatty-acid biosynthesis pathway of bacteria. Endogenous fatty acids are synthesized in all organisms in a pathway catalyzed by the fatty acid synthase complex. In bacteria, where the fatty acids are used primarily for incorporation into components of cell membranes, fatty acid synthase is made up of several independent cytoplasmic enzymes, each catalyzing one specific reaction. The initiation of the elongation step, which extends the length of the growing acyl chain by two carbons, requires the transfer of the malonyl moiety from malonyl-CoA onto the acyl carrier protein. The acyl carrier protein from Salmonella Typhimurium is similar to one from Escherichia coli. The protein has an alpha/beta type architecture, but its fold is unique. The active site inferred from the location of the catalytic Ser-92 contains a typical nucleophilic elbow as observed in alpha/beta hydrolases. Various binary complex structures of the Escherichia coli enzyme are reported. The obtained data from structural studies could be used in aiding the process of rational inhibitor design.