K. Yano et A. Zarainherzberg, SARCOPLASMIC-RETICULUM CALSEQUESTRINS - STRUCTURAL AND FUNCTIONAL-PROPERTIES, Molecular and cellular biochemistry, 135(1), 1994, pp. 61-70
Calsequestrin is the major Ca2+-binding protein localized in the termi
nal cisternae of the sarcoplasmic reticulum (SR) of skeletal and cardi
ac muscle cells. Calsequestrin has been purified and cloned from both
skeletal and cardiac muscle in mammalian, amphibian, and avian species
. Two different calsequestrin gene products namely cardiac and fast ha
ve been identified. Fast and cardiac calsequestrin isoforms have a hig
hly acidic amino acid composition. The amino acid composition of the c
ardiac form is very similar to the skeletal form expect for the carbox
yl terminal region of the protein which possess variable length of aci
dic residues and two phosphorylation sites. Circular dichroism and NMR
studies have shown that calsequestrin increases its alpha-helical con
tent and the intrinsic fluorescence upon binding of Ca2+. Calsequestri
n binds Ca2+ with high-capacity and with moderate affinity and its fun
ctions as a Ca2+ storage protein in the lumen of the SR. Calsequestrin
has been found to be associated with the Ca2+ release channel protein
complex of the SR through protein-protein interactions. The human and
rabbit fast calsequestrin genes have been cloned. The fast gene is sk
eletal muscle specific and transcribed at different rates in fast and
slow skeletal muscle but not in cardiac calsequestrin gene. This gene
is also expressed in slow skeletal muscle. No change in calsequestrin
mRNA expression has been detected in animal models of cardiac hypertro
phy and in failing human heart.