Snapshots of acyl carrier protein shuttling in human fatty acid synthase

The mammalian fatty acid synthase (FASN) enzyme is a dynamic multienzyme that belongs to the megasynthase family. In mammals, a single gene encodes six catalytically active domains and a flexibly tethered acyl carrier protein (ACP) domain that shuttles intermediates between active sites for fatty acid biosynthesis¹. FASN is an essential enzyme in mammalian development through the role that fatty acids have in membrane formation, energy storage, cell signalling and protein modifications. Thus, FASN is a promising target for treatment of a large variety of diseases including cancer, metabolic dysfunction-associated fatty liver disease, and viral and parasite infections^2,3. The multi-faceted mechanism of FASN and the dynamic nature of the protein, in particular of the ACP, have made it challenging to understand at the molecular level. Here we report cryo-electron microscopy structures of human FASN in a multitude of conformational states with NADPH and NADP⁺ plus acetoacetyl-CoA present, including structures with the ACP stalled at the dehydratase (DH) and enoyl-reductase (ER) domains. We show that FASN activity in vitro and de novo lipogenesis in cells is inhibited by mutations at the ACP-DH and ACP-ER interfaces. Together, these studies provide new molecular insights into the dynamic nature of FASN and the ACP shuttling mechanism, with implications for developing improved FASN-targeted therapeutics.