title: High-capacity Ca2+ binding of human skeletal calsequestrin.
abstract: Calsequestrin, the major calcium storage protein in both cardiac and skeletal muscle, binds large amounts of Ca(2+) in the sarcoplasmic reticulum and releases them during muscle contraction. For the first time, the crystal structures of Ca(2+) complexes for both human (hCASQ1) and rabbit (rCASQ1) skeletal calsequestrin were determined, clearly defining their Ca(2+) sequestration capabilities through resolution of high- and low-affinity Ca(2+)-binding sites. rCASQ1 crystallized in low CaCl(2) buffer reveals three high-affinity Ca(2+) sites with trigonal bipyramidal, octahedral, and pentagonal bipyramidal coordination geometries, along with three low-affinity Ca(2+) sites. hCASQ1 crystallized in high CaCl(2) shows 15 Ca(2+) ions, including the six Ca(2+) ions in rCASQ1. Most of the low-affinity sites, some of which are μ-carboxylate-bridged, are established by the rotation of dimer interfaces, indicating cooperative Ca(2+) binding that is consistent with our atomic absorption spectroscopic data. On the basis of these findings, we propose a mechanism for the observed in vitro and in vivo dynamic high-capacity and low-affinity Ca(2+)-binding activity of calsequestrin.
authors.affiliation: School of Molecular Biosciences, Washington State University, Pullman, Washington 99164, USA.
authors.forename: Emiliano J
authors.initials: EJ
authors.lastname: Sanchez
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Lewis
authors.forename: Benjamin R
authors.initials: BR
authors.lastname: Danna
authors.forename: Chulhee
authors.initials: C
authors.lastname: Kang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002155:Calsequestrin / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004285:Dogs; D006801:Humans; D008027:Light; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism*; D011485:Protein Binding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D011817:Rabbits; D012542:Scattering, Radiation
chemical_list: D002155:Calsequestrin; D002118:Calcium