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  • The EMBO Journal (2001) 20, 5060 - 5069
  • doi:10.1093/emboj/20.18.5060

Citrin and aralar1 are Ca2+-stimulated aspartate/glutamate transporters in mitochondria

L. Palmieri1, B. Pardo2, F.M. Lasorsa1, A. del Arco2,3, K. Kobayashi4, M. Iijima4, M.J. Runswick5, J.E. Walker5, T. Saheki4, J. Satrústegui2 and F. Palmieri1

  1. Department of Pharmaco-Biology, University of Bari, Via Orabona 4, 70125 Bari, Italy
  2. Departamento de Biologia Molecular, Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid, 28049 Madrid Spain
  3. Facultad de Ciencias del Medio Ambiente, Universidad de Castilla La Mancha, Toledo, Spain
  4. Department of Biochemistry, Faculty of Medicine, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima 890-8520, Japan
  5. The Medical Research Council, Dunn Human Nutrition Unit, Hills Road, Cambridge CB2 2XY, UK

Correspondence to:

F. Palmieri, E-mail: fpalm@farmbiol.uniba.it

Received 16 May 2001; Accepted 27 July 2001; Revised 27 June 2001

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 Ca2+-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 Ca2+ on the external side of the inner mitochondrial membrane, where the Ca2+-binding domains of these proteins are localized. These results show that the aspartate/glutamate carrier is regulated by Ca2+ through a mechanism independent of Ca2+ entry into mitochondria, and suggest a novel mechanism of Ca2+ regulation of the aspartate/malate shuttle.

  • Keywords:

    • aralar1,
    • aspartate,
    • glutamate carrier,
    • calcium,
    • citrin,
    • mitochondria