Amyotrophic Lateral Sclerosis-linked Glutamate Transporter Mutant Has Impaired Glutamate Clearance Capacity

• Published in: The Journal of biological chemistry 2001-01, Vol.276 (1), p.576-582
• Main Authors: Trotti, Davide, Aoki, Masashi, Pasinelli, Piera, Berger, Urs V., Danbolt, Niels C., Brown, Robert H., Hediger, Matthias A.
• Format: Article
• Language: English
• Subjects: Amino Acid Substitution - genetics; Amino Acid Transport System X-AG; Amyotrophic Lateral Sclerosis - genetics; Animals; ATP-Binding Cassette Transporters - genetics; ATP-Binding Cassette Transporters - metabolism; Biological Transport - drug effects; Cell Membrane - metabolism; COS Cells; Cytoplasm - metabolism; EAAC1 protein; Electric Conductivity; Fluorescent Antibody Technique; Genes, Dominant - genetics; glutamate transporter GLT1; Glutamic Acid - metabolism; Glycosylation; Humans; Kainic Acid - analogs & derivatives; Kainic Acid - pharmacology; Microinjections; Mutation - genetics; N206S protein; Oocytes - drug effects; Oocytes - metabolism; RNA, Complementary - genetics; Sodium Glutamate - administration & dosage; Sodium Glutamate - metabolism; Sodium Glutamate - pharmacology; Transfection; Xenopus laevis
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M003779200

We have investigated the functional impact of a naturally occurring mutation of the human glutamate transporter GLT1 (EAAT2), which had been detected in a patient with sporadic amyotrophic lateral sclerosis. The mutation involves a substitution of the putative N-linked glycosylation site asparagine 206 by a serine residue (N206S) and results in reduced glycosylation of the transporter and decreased uptake activity. Electrophysiological analysis of N206S revealed a pronounced reduction in transport rate compared with wild-type, but there was no alteration in the apparent affinities for glutamate and sodium. In addition, no change in the sensitivity for the specific transport inhibitor dihydrokainate was observed. However, the decreased rate of transport was associated with a reduction of the N206S transporter in the plasma membrane. Under ionic conditions, which favor the reverse operation mode of the transporter, N206S exhibited an increased reverse transport capacity. Furthermore, if coexpressed in the same cell, N206S manifested a dominant negative effect on the wild-type GLT1 activity, whereas it did not affect wild-type EAAC1. These findings provide evidence for a role of the N-linked glycosylation in both cellular trafficking and transport function. The resulting alteration in glutamate clearance capacity likely contributes to excitotoxicity that participates in motor neuron degeneration in amyotrophic lateral sclerosis.