The mitochondrial oxoglutarate carrier: from identification to mechanism

Abstract

The 2-oxoglutarate carrier (OGC) belongs to the mitochondrial carrier protein family whose members are responsible for the exchange of metabolites, cofactors and nucleotides between the cytoplasm and mitochondrial matrix. Initially, OGC was characterized by determining substrate specificity, kinetic parameters of transport, inhibitors and molecular probes that form covalent bonds with specific residues. It was shown that OGC specifically transports oxoglutarate and certain carboxylic acids. The substrate specificity combination of OGC is unique, although many of its substrates are also transported by other mitochondrial carriers. The abundant recombinant expression of bovine OGC in Escherichia coli and its ability to functionally reconstitute into proteoliposomes made it possible to deduce the individual contribution of each and every residue of OGC to the transport activity by a complete set of cys-scanning mutants. These studies give experimental support for a substrate binding site constituted by three major contact points on the even-numbered α-helices and identifies other residues as important for transport function through their crucial positions in the structure for conserved interactions and the conformational changes of the carrier during the transport cycle. The results of these investigations have led to utilize OGC as a model protein for understanding the transport mechanism of mitochondrial carriers.

Fe-S Cluster Biogenesis in Isolated Mammalian Mitochondria

“…3A, lanes 1-7). Note that such a treatment did not alter the amount of available endogenous apoACO2, as judged by the levels of ACO2 [Fe- When added to intact mitochondria, ␣KG can efficiently enter into the matrix by the 2-oxoglutarate transporter and/or the dicarboxylate carrier protein in the inner membrane (27) and be utilized by ␣KG dehydrogenase to form succinyl-CoA (28). Succinyl-CoA, in turn, is converted to succinate by succinyl-CoA synthetase as part of the mitochondrial Krebs cycle.…”

Mitochondrial tricarboxylate and dicarboxylate–Tricarboxylate carriers: from animals to plants

“…Some activity has also been observed with succinate . The CiC overlaps with oxoglutarate carrier (OGC) by transporting the substrate malate and malonate . In yeast, a second isoform of CiC (CiC2, also known as YHM2) has been identified that differs markedly from the yeast CiC (CiC1) previously identified in this organism as this protein efficiently transports citrate, oxoglutarate oxaloacetate, succinate, and fumarate, whereas different from CiC1 the reconstituted CiC2 transports isocitrate, cis ‐aconitate, and malate with very low efficiency .…”

Metabolic flux analysis of Saccharomyces cerevisiae during redox potential–controlled very high‐gravity ethanol fermentation

“…Controlling fermentation redox potential may indirectly alter redox balancing in yeast, resulting in different ethanol productivity . We postulate that the variation of extracellular redox environment might affect intracellular functionality and efficiency of aspartate–glutamate carrier, α‐ketoglutarate (AKG) carrier, citrate carrier, and glutamate carrier in the shuttle . In addition to the TCA cycle, the malate–aspartate shuttle provides another passage to allow NADH in the cytosol to be oxidized and transfer electrons to NAD + inside the mitochondria to maintain a redox‐balanced environment .…”