Uncovering the Hidden Role of 2-Oxoglutarate/Malate Carrier in Uncoupling: Implications for Metabolic Disorders and Cancer

The mitochondrial 2-oxoglutarate/malate carrier (α-ketoglutarate/malate carrier, OGC) transports 2-oxoglutarate for malate across the inner mitochondrial membrane and plays a crucial role in the malate-aspartate shuttle. OGC is ubiquitously expressed in healthy and cancerous tissues, and its gene knockout is embryonically lethal. Despite sharing a high homology with other proteins from the solute carrier 25 family (adenine nucleotide translocase 1 and uncoupling proteins 1-3 that facilitate proton transport mediated by free fatty acids (FAs), the role of OGC in uncoupling has never been studied in a well-defined system. We hypothesized that OGC can directly enhance proton transport in the presence of FAs. To test this, we produced OGC in E. coli and reconstituted it in liposomes. Our experiments show that reconstituted OGC increases the specific membrane conductance of lipid bilayer membranes only in the presence of FAs, proving its involvement in proton transport. OGC's substrates and substrate analogs inhibited this effect, suggesting competition for the same binding site in the protein's cavity. Site-directed mutagenesis revealed that R90 is involved in the FA-mediated proton leak, suggesting a common binding site for substrates and FAs. Understanding the molecular mechanism and role of OGC in uncoupling could have important implications for the development of targeted drug delivery systems for the treatment of metabolic disorders, obesity, and cancer.