Understanding the Catalytic Machinery and the Reaction Pathway of the Malonyl-Acetyl Transferase Domain of Human Fatty Acid Synthase

Abstract

Human fatty acid synthase (hFAS) is a large multienzyme that catalyzes all steps of fatty acid synthesis, which is overexpressed in many cancer cells. Studies have shown that FAS inhibitors exhibit antitumor activity without relevant effects over normal cells. Therefore, the molecular description of active sites in hFAS should stimulate the development of inhibitors as anticancer drug candidates. The malonyl-acetyl transferase (MAT) domain is responsible for loading acetyl-CoA and malonyl-CoA substrates to the acyl-carrier protein (ACP) domain, a carrier for fatty acid reaction intermediates. In this work, we have applied computational QM/MM methods at the DLPNO–CCSD(T)/CBS:AMBER level of theory to study the MAT reaction mechanism. The results indicate that the initial catalytic stage occurs in two sequential steps: (1) nucleophilic attack on the thioester carbonyl group of the substrate through a concerted pathway that involves a Ser-His dyad and (2) tetrahedral intermediate breakdown and release of the ...