Functional reconstitution of the mitochondrial Ca2+/H+ antiporter Letm1
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CitationTsai, Ming-Feng, Dawei Jiang, Linlin Zhao, David Clapham, and Christopher Miller. 2014. “Functional reconstitution of the mitochondrial Ca2+/H+ antiporter Letm1.” The Journal of General Physiology 143 (1): 67-73. doi:10.1085/jgp.201311096. http://dx.doi.org/10.1085/jgp.201311096.
AbstractThe leucine zipper, EF hand–containing transmembrane protein 1 (Letm1) gene encodes a mitochondrial inner membrane protein, whose depletion severely perturbs mitochondrial Ca2+ and K+ homeostasis. Here we expressed, purified, and reconstituted human Letm1 protein in liposomes. Using Ca2+ fluorophore and 45Ca2+-based assays, we demonstrate directly that Letm1 is a Ca2+ transporter, with apparent affinities of cations in the sequence of Ca2+ ≈ Mn2+ > Gd3+ ≈ La3+ > Sr2+ >> Ba2+, Mg2+, K+, Na+. Kinetic analysis yields a Letm1 turnover rate of 2 Ca2+/s and a Km of ∼25 µM. Further experiments show that Letm1 mediates electroneutral 1 Ca2+/2 H+ antiport. Letm1 is insensitive to ruthenium red, an inhibitor of the mitochondrial calcium uniporter, and CGP-37157, an inhibitor of the mitochondrial Na+/Ca2+ exchanger. Functional properties of Letm1 described here are remarkably similar to those of the H+-dependent Ca2+ transport mechanism identified in intact mitochondria.
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