Functional and structural role of amino acid residues in the matrix alpha-helices, termini and cytosolic loops of the bovine mitochondrial oxoglutarate carrier.

The mitochondrial oxoglutarate carrier belongs to the mitochondrial carrier family and exchanges oxoglutarate for malate and other dicarboxylates across the mitochondrial inner membrane. Here, single-cysteine mutant carriers were engineered for every residue in the amino- and carboxy-terminus, cytoplasmic loops, and matrix alpha-helices and their transport activity was measured in the presence and absence of sulfhydryl reagents. The analysis of the cytoplasmic side of the oxoglutarate carrier showed that the conserved and symmetric residues of the mitochondrial carrier motif [DE]XX[RK] localized at the C-terminal end of the even-numbered transmembrane alpha-helices are important for the function of the carrier, but the non-conserved cytoplasmic loops and termini are not.

Functional and structural role of amino acid residues in the odd-numbered transmembrane alpha-helices of the bovine mitochondrial oxoglutarate carrier.

The mitochondrial oxoglutarate carrier (OGC) plays an important role in the malate-aspartate shuttle, the oxoglutarate-isocitrate shuttle and gluconeogenesis. To establish amino acid residues that are important for function, each residue in the transmembrane alpha-helices H1, H3 and H5 was replaced systematically by a cysteine in a fully functional mutant carrier that was devoid of cysteine residues. The transport activity of the mutant carriers was measured in the presence and absence of sulfhydryl reagents.

Substrate-induced conformational changes of the mitochondrial oxoglutarate carrier: a spectroscopic and molecular modelling study.

The structural and dynamic properties of the oxoglutarate carrier were investigated by introducing a single tryptophan in the Trp-devoid carrier in position 184, 190 or 199 and by monitoring the fluorescence spectra in the presence and absence of the substrate oxoglutarate. In the absence of substrate, the emission maxima of Arg190Trp, Cys184Trp and Leu199Trp are centered at 342, 345 and 348 nm, respectively, indicating that these residues have an increasing degree of solvent exposure. The emission intensity of the Arg190Trp and Cys184Trp mutants is higher than that of Leu199Trp.