Uncoupling protein 3 adjusts mitochondrial Ca(2+) uptake to high and low Ca(2+) signals.
Uncoupling proteins 2 and 3 (UCP2/3) are essential for mitochondrial Ca(2+) uptake but both proteins exhibit distinct activities in regard to the source and mode of Ca(2+) mobilization. In the present work, structural determinants of their contribution to mitochondrial Ca(2+) uptake were explored. Previous findings indicate the importance of the intermembrane loop 2 (IML2) for the contribution of UCP2/3. Thus, the IML2 of UCP2/3 was substituted by that of UCP1. These chimeras had no activity in mitochondrial uptake of intracellularly released Ca(2+), while they mimicked the wild-type proteins by potentiating mitochondrial sequestration of entering Ca(2+). Alignment of the IML2 sequences revealed that UCP1, UCP2 and UCP3 share a basic amino acid in positions 163, 164 and 167, while only UCP2 and UCP3 contain a second basic residue in positions 168 and 171, respectively. Accordingly, mutants of UCP3 in positions 167 and 171/172 were made. In permeabilized cells, these mutants exhibited distinct Ca(2+) sensitivities in regard to mitochondrial Ca(2+) sequestration. In intact cells, these mutants established different activities in mitochondrial uptake of either intracellularly released (UCP3(R171,E172)) or entering (UCP3(R167)) Ca(2+). Our data demonstrate that distinct sites in the IML2 of UCP3 effect mitochondrial uptake of high and low Ca(2+) signals.
Institute of Molecular Biology and Biochemistry, Centre of Molecular Medicine, Medical University of Graz, Harrachgasse 21/III, 8010 Graz, Austria.
Markus
M
Waldeck-Weiermair
Xiumei
X
Duan
Shamim
S
Naghdi
Muhammad Jadoon
MJ
Khan
Michael
M
Trenker
Roland
R
Malli
Wolfgang F
WF
Graier
D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002460:Cell Line; D006801:Humans; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D000071246:Uncoupling Protein 2; D000071247:Uncoupling Protein 3
D007473:Ion Channels; D026901:Membrane Transport Proteins; D024101:Mitochondrial Proteins; C000604389:UCP2 protein, human; C000604392:UCP3 protein, human; D000071246:Uncoupling Protein 2; D000071247:Uncoupling Protein 3; D002118:Calcium