Structural highlights
Function[CASQ1_HUMAN] Calsequestrin is a high-capacity, moderate affinity, calcium-binding protein and thus acts as an internal calcium store in muscle. Calcium ions are bound by clusters of acidic residues at the protein surface, often at the interface between subunits. Can bind around 80 Ca(2+) ions. Regulates the release of lumenal Ca(2+) via the calcium release channel RYR1; this plays an important role in triggering muscle contraction.[1] [2] Publication Abstract from PubMedCalsequestrin, the major calcium-storage protein of both cardiac and skeletal muscle, binds large amounts of Ca2+ in the sarcoplasmic reticulum and releases them during muscle contraction. For the first time, crystal structures of Ca2+-complexes for both human (hCASQ1) and rabbit skeletal calsequestrin (rCASQ1) were determined, clearly defining its Ca2+-sequestration capabilities through resolution of high- and low-affinity Ca2+-binding sites. rCASQ1 crystallized in low CaCl2 buffer revealed three high-affinity Ca2+ sites with trigonal bipyramidal, octahedral, and pentagonal bipyramidal coordination geometries, along with three low-affinity Ca2+ sites. hCASQ1 crystallized in high CaCl2 showed fifteen Ca2+ ions, which included the six Ca2+ ions in rCASQ1. Most of the low-affinity sites, some of which were mu-carboxylate-bridged, were established by the rotation of dimeric interfaces, indicating cooperative Ca2+-binding that is consistent with our atomic absorption spectroscopic data. Based on these findings, we propose a mechanism for the observed in vitro and in vivo dynamic high-capacity and low-affinity Ca2+-binding activity of calsequestrin. High-capacity Ca2+-binding of human skeletal calsequestrin.,Sanchez EJ, Lewis KM, Danna BR, Kang C J Biol Chem. 2012 Feb 15. PMID:22337878[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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