Identification of a novel human subfamily of mitochondrial carriers with calcium-binding domains.
Aralar1 and citrin were identified as calcium binding aspartate/glutamate carriers (AGC) in mitochondria. The presence of calcium binding motifs facing the extramitochondrial space allows the regulation of the transport activity of these carriers by cytosolic calcium and provides a new mechanism to transduce calcium signals in mitochondria without the requirement of calcium entry in the organelle. We now report the complete characterization of a second subfamily of human calcium binding mitochondrial carriers named SCaMC (short calcium-binding mitochondrial carriers). We have identified three SCaMC genes in the human genome. All code for highly conserved proteins (about 70-80% identity), of about 500 amino acids with a characteristic mitochondrial carrier domain at the C terminus, and an N-terminal extension harboring four EF-hand binding motifs with high similarity to calmodulin. All SCaMC proteins were found to be located exclusively in mitochondria, and their N-terminal extensions were dispensable for the correct mitochondrial targeting of the polypeptides. SCaMC-1 is the human orthologue of the rabbit Efinal protein, which was reported to be located in peroxisomes, and SCaMC-2 is the human orthologue of the rat MCSC protein, described as up-regulated by dexamethasone in AR42J cells. One of the SCaMC genes, SCaMC-2, has four variants generated by alternative splicing, resulting in proteins with a common C terminus but with variations in their N-terminal halves, including the loss of one to three EF-hand motifs. These results make SCaMC one of most complex subfamilies of mitochondrial carriers and suggest that the large number of isoforms and splice variants may confer different calcium sensitivity to the transport activity of these carriers.
del Arco
Araceli
A
Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa, Facultad de Ciencias, Universidad Autónoma, 28049 Madrid, Spain. adelarco@cbm.uam.es
Satrústegui
Jorgina
J
D017398:Alternative Splicing; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D026905:Amino Acid Transport Systems; D026922:Amino Acid Transport Systems, Acidic; D000818:Animals; D017920:Antiporters; D015152:Blotting, Northern; D015153:Blotting, Western; D019556:COS Cells; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000502:physiology; D002147:Calmodulin / Q000737:chemistry; D002460:Cell Line; D018076:DNA, Complementary / Q000378:metabolism; D019992:Databases as Topic; D003907:Dexamethasone / Q000494:pharmacology; D005091:Exons; D020224:Expressed Sequence Tags; D015894:Genome, Human; D006801:Humans; D015151:Immunoblotting; D007438:Introns; D008168:Lung / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000502:physiology; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D024101:Mitochondrial Proteins / Q000502:physiology; D008969:Molecular Sequence Data; D005810:Multigene Family; D027361:Organic Anion Transporters / Q000502:physiology; D010455:Peptides / Q000737:chemistry; D020675:Peroxisomes / Q000378:metabolism; D010802:Phylogeny; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution; D015854:Up-Regulation
D026905:Amino Acid Transport Systems; D026922:Amino Acid Transport Systems, Acidic; D017920:Antiporters; D002135:Calcium-Binding Proteins; D002147:Calmodulin; D018076:DNA, Complementary; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D024101:Mitochondrial Proteins; D027361:Organic Anion Transporters; D010455:Peptides; D020033:Protein Isoforms; C114606:SLC25A12 protein, human; C487500:SLC25A24 protein, human; C487501:SLC25A25 protein, human; C487502:SLC25A26 protein, human; C491957:Slc25a12 protein, rat; C008822:citrin; D003907:Dexamethasone; D002118:Calcium