1SJI

Comparing skeletal and cardiac calsequestrin structures and their calcium binding: a proposed mechanism for coupled calcium binding and protein polymerization

Summary for 1SJI

• Entry DOI: 10.2210/pdb1sji/pdb
• Descriptor: Calsequestrin, cardiac muscle isoform (2 entities in total)
• Functional Keywords: calsequestrin, glycoprotein, calcium-binding, muscle protein, metal binding protein
• Biological source: Canis lupus familiaris (dog)
• Cellular location: Sarcoplasmic reticulum lumen : P12637
• Total number of polymer chains: 2
• Total formula weight: 81491.71

Authors

Park, H.J.,Park, I.Y.,Kim, E.J.,Youn, B.,Fields, K.,Dunker, A.K.,Kang, C.H. (deposition date: 2004-03-03, release date: 2005-03-15, Last modification date: 2024-02-14)

Primary citation

Park, H.J.,Park, I.Y.,Kim, E.J.,Youn, B.,Fields, K.,Dunker, A.K.,Kang, C.H.
Comparing skeletal and cardiac calsequestrin structures and their calcium binding: a proposed mechanism for coupled calcium binding and protein polymerization.
J.Biol.Chem., 279:18026-18033, 2004

PubMed Abstract: Calsequestrin, the major calcium storage protein of both cardiac and skeletal muscle, binds and releases large numbers of Ca(2+) ions for each contraction and relaxation cycle. Here we show that two crystal structures for skeletal and cardiac calsequestrin are nearly superimposable not only for their subunits but also their front-to-front-type dimers. Ca(2+) binding curves were measured using atomic absorption spectroscopy. This method enables highly accurate measurements even for Ca(2+) bound to polymerized protein. The binding curves for both skeletal and cardiac calsequestrin were complex, with binding increases that correlated with protein dimerization, tetramerization, and oligomerization. The Ca(2+) binding capacities of skeletal and cardiac calsequestrin are directly compared for the first time, with approximately 80 Ca(2+) ions bound per skeletal calsequestrin and approximately 60 Ca(2+) ions per cardiac calsequestrin, as compared with net charges for these molecules of -80 and -69, respectively. Deleting the negatively charged and disordered C-terminal 27 amino acids of cardiac calsequestrin results in a 50% reduction of its calcium binding capacity and a loss of Ca(2+)-dependent tetramer formation. Based on the crystal structures of rabbit skeletal muscle calsequestrin and canine cardiac calsequestrin, Ca(2+) binding capacity data, and previous light-scattering data, a mechanism of Ca(2+) binding coupled with polymerization is proposed.

PubMed: 14871888
DOI: 10.1074/jbc.M311553200

Experimental method

X-RAY DIFFRACTION (2.4 Å)