Molecular identification and functional characterization of a novel glutamate transporter in yeast and plant mitochondria.

The genome of S. cerevisiae encodes 35 members of the mitochondrial carrier family (MCF) and that of A. thaliana 58 MCF members. Here two members of this family, Ymc2p from S. cerevisiae and BOU from Arabidopsis, have been characterized. These proteins were overproduced in bacteria and reconstituted into liposomes. Their transport properties and kinetic parameters demonstrate that Y mc2p and BOU transport glutamate. Transport catalyzed by both carriers was saturable, inhibited by mercuric chloride and dependent on the proton gradient across the proteoliposomal membrane. The growth phenotype of S. cerevisiae cells lacking the genes ymc2 and agcl, which encodes the only other S. cerevisiae carrier capable to transport also glutamate, was fully complemented by expressing Ymc2p, Agclp or BOU. Furthermore, mitochondria isolated from wild-type, ymc2f,,, and agcl /j,, strains, but not from the double mutant ymc2f,,,agcl /j,, strain, swell in isosmotic ammonium glutamate showing that glutamate is transported together with a W. lt is proposed that the primary function of these proteins is to import glutamate into the mitochondrial matrix for energy production, Cl metabolism and protein synthesis.