GENOMICS PROTEOMICS AND BIOINFORMATICS
Identification of the Mitochondrial Glutamate Transporter: BACTERIAL EXPRESSION, RECONSTITUTION, FUNCTIONAL CHARACTERIZATION, AND TISSUE DISTRIBUTION OF TWO HUMAN ISOFORMS*

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The mitochondrial carriers are a family of transport proteins in the inner membranes of mitochondria. They shuttle substrates, metabolites, and cofactors through this membrane and connect cytoplasm functions with others in the matrix. Glutamate is co-transported with H+ (or exchanged for OH−), but no protein has ever been associated with this activity. Two human expressed sequence tags encode proteins of 323 and 315 amino acids with 63% identity that are related to the aspartate-glutamate carrier, a member of the carrier family. They have been overexpressed in Escherichia coli and reconstituted into phospholipid vesicles. Their transport properties demonstrate that the two proteins are isoforms of the glutamate/H+ symporter described in the past in whole mitochondria. Isoform 1 is expressed at higher levels than isoform 2 in all the tissues except in brain, where the two isoforms are expressed at comparable levels. The differences in expression levels and kinetic parameters of the two isoforms suggest that isoform 2 matches the basic requirement of all tissues especially with respect to amino acid degradation, and isoform 1 becomes operative to accommodate higher demands associated with specific metabolic functions such as ureogenesis.

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Published, JBC Papers in Press, March 15, 2002, DOI 10.1074/jbc.M201572200

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This work was supported by Ministero dell'Università e della Ricerca Scientifica e Tecnologica, by MURST L.488/92 CO3 and CO4 and MURST-CNR L.95/95, by the Centro di Eccellenze di Genomica Comparate, University of Bari, by the Consiglio Nazionale delle Ricerche target project on Biotechnology, and by the European Social Fund. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

This paper is dedicated to the memory of Professor Vincenzo Bocchini.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EBI Data Bank with accession number(s),

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© 2002 ASBMB. Currently published by Elsevier Inc; originally published by American Society for Biochemistry and Molecular Biology.