Calsequestrin is a calcium-binding protein of the sarcoplasmic reticulum. The protein helps hold calcium in the cisterna of the sarcoplasmic reticulum after a muscle contraction, even though the concentration of calcium in the sarcoplasmic reticulum is much higher than in the cytosol. It also helps the sarcoplasmic reticulum store an extraordinarily high amount of calcium ions. Each molecule of calsequestrin can bind 18 to 50 Ca2+ ions.  Sequence analysis has suggested that calcium is not bound in distinct pockets via EF-hand motifs, but rather via presentation of a charged protein surface. Two forms of calsequestrin have been identified. The cardiac form (Calsequestrin-2/CASQ2) is present in cardiac and slow skeletal muscle and the fast skeletal form (Calsequestrin-1/CASQ1) is found in fast skeletal muscle. The release of calsequestrin-bound calcium (through a calcium release channel) triggers muscle contraction. The active protein is not highly structured, more than 50% of it adopting a random coil conformation. When calcium binds there is a structural change whereby the alpha-helical content of the protein increases from 3 to 11%. Both forms of calsequestrin are phosphorylated by casein kinase 2, but the cardiac form is phosphorylated more rapidly and to a higher degree. Calsequestrin is also secreted in the gut where it deprives bacteria of calcium ions.
- ^ Katz, Arnold M. (2005). Physiology of the Heart (4th ed.). Lippincott Williams & Wilkins. p. 192. ISBN 0-7817-5501-8.
- ^ a b Slupsky JR, Ohnishi M, Carpenter MR, Reithmeier RA (October 1987). "Characterization of cardiac calsequestrin". Biochemistry 26 (20): 6539–44. PMID 3427023. doi:10.1021/bi00394a038.
- ^ Cala SE, Jones LR (January 1991). "Phosphorylation of cardiac and skeletal muscle calsequestrin isoforms by casein kinase II. Demonstration of a cluster of unique rapidly phosphorylated sites in cardiac calsequestrin". J. Biol. Chem. 266 (1): 391–8. PMID 1985907.
- Wang S, Trumble WR, Liao H, Wesson CR, Dunker AK, Kang CH (1998). "Crystal structure of calsequestrin from rabbit skeletal muscle sarcoplasmic reticulum". Nat. Struct. Biol. 5 (6): 476–83. PMID 9628486. doi:10.1038/nsb0698-476.
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This article incorporates text from the public domain Pfam and InterPro IPR001393