Specific Interaction of the Human Mitochondrial Uncoupling Protein 1 with Free Long-Chain Fatty Acid.

The mitochondrial uncoupling protein 1 (UCP1) generates heat by causing proton leak across the mitochondrial inner membrane that requires fatty acid (FA). The mechanism by which UCP1 uses FA to conduct proton remains unsolved, and it is also unclear whether a direct physical interaction between UCP1 and FA exists. Here, we have shown using nuclear magnetic resonance that FA can directly bind UCP1 at a helix-helix interface site composed of residues from the transmembrane helices H1 and H6. According to the paramagnetic relaxation enhancement data and molecular dynamics simulation, the FA acyl chain appears to fit into the groove between H1 and H6 while the FA carboxylate group interacts with the basic residues near the matrix side of UCP1. Functional mutagenesis showed that mutating the observed FA binding site severely reduced UCP1-mediated proton flux. Our study identifies a functionally important FA-UCP1 interaction that is potentially useful for mechanistic understanding of UCP1-mediated thermogenesis.