Structural basis of fatty acid activation and transport by human FATP2

Abstract

Fatty acids (FAs) are essential biomolecules that play critical roles in development and growth. Fatty acid transport proteins (FATPs) are responsible for the transport of long-chain FAs (LCFAs) and very-long-chain FAs (VLCFAs), exhibiting bifunctionality that includes both FA transport and acyl-CoA synthetase activity. FATPs are potential drug targets for treating various metabolism-related diseases, including cancers. However, the lack of three-dimensional structures of FATPs has hindered our understanding of their mechanisms. Here, we report a cryo-EM structure of human FATP2 in complex with an acyl-AMP intermediate and an incoming FA substrate at 2.9 Å resolution. The FA substrate, adopting a crescent shape, interacts with the membrane and a reclining membrane-associated helix of FATP2, with its tail half inserted into the membrane and its head half bound to a hydrophobic pocket on FATP2 at the protein-membrane interface. The acyl-AMP is bound below the FA substrate, with the AMP portion in a large central pocket and the acyl group in a hydrophobic tunnel that connects the FA entry pocket and the central pocket. This structure reveals that the FA substrate from the membrane may undergo a two-step translocation process to access the catalytic center. The spacious inner cavity allows the binding of a new FA substrate before the completion of a full reaction cycle, which may be a crucial mechanism to ensure the catalytic and transport efficiency of FATP2. We also demonstrate that FATP2 transport FAs, strictly dependent on the activation of FAs through the acyl-CoA synthetase activity of FATP2. Our findings provide important insights into the catalytic and transport mechanisms of FATPs and offer a structural basis for the development of inhibitors targeting FATPs to treat related diseases.