Characterization of cardiac calsequestrin.
Calsequestrin, a calcium-binding protein found in the sarcoplasmic reticulum of muscle cells, was purified from rabbit and canine cardiac and skeletal muscle tissue. The amino acid compositions and amino-terminal sequences of skeletal and cardiac calsequestrin from rabbit and dog were determined. The amino acid composition of the cardiac form was very similar to the skeletal form. The amino-terminal sequence of the cardiac form was homologous to, but not identical with, the amino-terminal sequence of the skeletal form of the protein. Few species differences in the amino-terminal sequences were observed. The calcium-binding capacity of the cardiac form was half the capacity of the skeletal form although the affinities of the two forms of calsequestrin for Ca2+ were similar (Kd = 1 mM). Calcium binding to the cardiac form induced structural changes in the protein as determined by circular dichroism and intrinsic fluorescence spectroscopy. The alpha-helical content of cardiac calsequestrin increased from 3.5% to 10.9% upon binding calcium, while the intrinsic fluorescence of the protein increased 14%. Potassium ions also affected the conformation of cardiac calsequestrin.
Department of Biochemistry, University of Alberta, Edmonton, Canada.
J R
JR
Slupsky
M
M
Ohnishi
M R
MR
Carpenter
R A
RA
Reithmeier
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002155:Calsequestrin / Q000302:isolation & purification* / Q000378:metabolism; D004285:Dogs; D009124:Muscle Proteins / Q000302:isolation & purification*; D009132:Muscles / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D009928:Organ Specificity; D011817:Rabbits; D013045:Species Specificity
D002155:Calsequestrin; D009124:Muscle Proteins; D002118:Calcium