3us3
Recombinant rabbit skeletal calsequestrin-MPD complexRecombinant rabbit skeletal calsequestrin-MPD complex
Structural highlights
Function[CASQ1_RABIT] Calsequestrin is a high-capacity, moderate affinity, calcium-binding protein and thus acts as an internal calcium store in muscle. The release of calcium bound to calsequestrin through a calcium release channel triggers muscle contraction. The skeletal muscle isoform (CASQ1) binds around 80 Ca(2+) ions, while the cardiac isoform (CASQ2) binds approximately 60 Ca(2+) ions (By similarity). Publication Abstract from PubMedCalsequestrin (CASQ) serves as a major Ca2+-storage/buffer protein in the sarcoplasmic reticulum (SR). When purified from skeletal muscle, CASQ1 is obtained in its glycosylated form. Here, we have confirmed the specific site and degree of glycosylation of native rabbit CASQ1 (rCASQ1), and have investigated its effect on critical properties of CASQ by comparison with the non-glycosylated recombinant form. Based on our comparative approach utilizing crystal structures, Ca2+-binding capacities, analytical ultracentrifugation, and light scattering profiles of the native and recombinant rCASQ1, we propose a novel and dynamic role for glycosylation in CASQ. CASQ undergoes a unique degree of mannose trimming as it is trafficked from the proximal ER to the SR. The major glycoform of CASQ (GlcNAc2Man9) found in the proximal ER can severely hinder formation of the back-to-back interface, potentially preventing premature Ca2+-dependent polymerization of CASQ, and ensuring its continuous mobility to the SR. Only trimmed glycans can stabilize both front-to-front and the back-to-back interfaces of CASQ through extensive hydrogen bonding and electrostatic interactions. Therefore, the mature glycoform of CASQ (GlcNAc2Man1-4) within the SR can be retained upon establishing a functional high-capacity Ca2+-binding polymer. In addition, based on the high-resolution structures, we propose a molecular mechanism for the catecholaminergic polymorphic ventricular tachycardia (CPVT2) mutation, K206N. Glycosylation of skeletal calsequestrin, implications for its function.,Sanchez EJ, Lewis KM, Munske GR, Nissen MS, Kang C J Biol Chem. 2011 Dec 14. PMID:22170046[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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