Citrin and aralar1 are Ca(2+)-stimulated aspartate/glutamate transporters in mitochondria

EMBO J. 2001 Sep 17;20(18):5060-9. doi: 10.1093/emboj/20.18.5060.

Abstract

The mitochondrial aspartate/glutamate carrier catalyzes an important step in both the urea cycle and the aspartate/malate NADH shuttle. Citrin and aralar1 are homologous proteins belonging to the mitochondrial carrier family with EF-hand Ca(2+)-binding motifs in their N-terminal domains. Both proteins and their C-terminal domains were overexpressed in Escherichia coli, reconstituted into liposomes and shown to catalyze the electrogenic exchange of aspartate for glutamate and a H(+). Overexpression of the carriers in transfected human cells increased the activity of the malate/aspartate NADH shuttle. These results demonstrate that citrin and aralar1 are isoforms of the hitherto unidentified aspartate/glutamate carrier and explain why mutations in citrin cause type II citrullinemia in humans. The activity of citrin and aralar1 as aspartate/glutamate exchangers was stimulated by Ca(2+) on the external side of the inner mitochondrial membrane, where the Ca(2+)-binding domains of these proteins are localized. These results show that the aspartate/glutamate carrier is regulated by Ca(2+) through a mechanism independent of Ca(2+) entry into mitochondria, and suggest a novel mechanism of Ca(2+) regulation of the aspartate/malate shuttle.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Transport Systems, Acidic*
  • Antiporters*
  • Calcium / pharmacology*
  • Calcium-Binding Proteins / genetics
  • Calcium-Binding Proteins / physiology*
  • Carrier Proteins / genetics
  • Carrier Proteins / physiology*
  • Cell Line
  • Citrullinemia / etiology*
  • Escherichia coli / genetics
  • Humans
  • Kinetics
  • Membrane Transport Proteins*
  • Mitochondria / metabolism*
  • Mitochondrial Membrane Transport Proteins
  • Mitochondrial Proteins*
  • Models, Chemical
  • Organic Anion Transporters*
  • Proteolipids / metabolism
  • Transfection

Substances

  • Amino Acid Transport Systems, Acidic
  • Antiporters
  • Calcium-Binding Proteins
  • Carrier Proteins
  • Membrane Transport Proteins
  • Mitochondrial Membrane Transport Proteins
  • Mitochondrial Proteins
  • Organic Anion Transporters
  • Proteolipids
  • SLC25A12 protein, human
  • aspartate-glutamate carrier
  • proteoliposomes
  • citrin
  • Calcium