Activation of the cardiac Na(+)-Ca(2+) exchanger by sorcin via the interaction of the respective Ca(2+)-binding domains.
Bottom Line: To investigate the importance of this region in the interaction with NCX1, three variants were examined: W105G and W99G, mutated respectively near EF3 and EF2, and E124A that does not bind Ca(2+) due to a mutation at EF3.Downregulation of sorcin decreased and supplementation with wt sorcin (3muM) increased NCX activity in isolated cardiomyocytes.The relative stimulatory effects of the sorcin variants were: W105G>wt sorcin>Sorcin Calcium Binding Domain (SCBD)>W99G>E124A.
Affiliation: C.N.R. Institute of Molecular Biology and Pathology, Department of Biochemical Sciences A. Rossi Fanelli, Sapienza University of Rome, 00185 Rome, Italy. email@example.comShow MeSH
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Mentions: Sorcin (soluble resistance-related calcium binding protein) is a 21.6 kDa protein identified in the cytosol of multidrug resistant cells [1,2] that belongs to the penta-EF-hand (PEF) family, a small group of regulatory calcium binding proteins comprising calpain, ALG-2, grancalcin, peflin and PEF1 [3–8]. Sorcin shares the typical structural and functional features of all PEF family members. It has a two-domain architecture, characterized by a flexible and hydrophobic Gly/Pro-rich N-terminal domain and a C-terminal calcium binding domain containing the five EF-hand motifs (Fig. 1), and dimerizes through the unpaired EF5 hand. Like the other PEF proteins, sorcin undergoes a Ca2+-dependent activation that promotes translocation to membranes where interaction with several molecular targets occurs . In turn, these features render sorcin an effective participant in a number of Ca2+-mediated processes. Sorcin activation is induced by Ca2+ binding to the two functionally relevant EF3 and EF2 motifs, that are not paired structurally as in most EF-hand proteins, but are connected by the long and rigid D helix (Fig. 1). An essential step of sorcin activation therefore consists in the transfer of information concerning Ca2+ binding from the site with the highest affinity for the metal, EF3, through the D helix to EF2, and from there to the rest of the molecule. The ensuing conformational change is believed to loosen the hydrophobic and hydrophilic interactions that bring the N- and C-terminal domains together. This renders both domains available for target protein recognition, in particular the D helix residues . It follows that the EF3-D helix-EF2 region should be considered as a tightly coupled functional unit.
Affiliation: C.N.R. Institute of Molecular Biology and Pathology, Department of Biochemical Sciences A. Rossi Fanelli, Sapienza University of Rome, 00185 Rome, Italy. firstname.lastname@example.org