Calsequestrin
Encyclopedia
Calsequestrin is a calcium-binding protein
of the sarcoplasmic reticulum. The protein helps hold calcium in the cisterna
of the sarcoplasmic reticulum after a muscle contraction, even though the concentration of calcium in the sarcoplasmic reticulum is much higher than in the cytosol. It also helps the sarcoplasmic reticulum store an extraordinarily high amount of calcium ions. Each molecule of calsequestrin can bind 18 to 50 Ca2+ ions. Sequence
analysis has suggested that calcium is not bound in distinct pockets via EF-hand motifs, but rather via presentation of a charged protein surface. Two forms of calsequestrin have been identified. The cardiac form (Calsequestrin-2/CASQ2) is present in cardiac and slow skeletal muscle and the fast skeletal form (Calsequestrin-1/CASQ1) is found in fast skeletal muscle. The release of calsequestrin-bound calcium (through a a calcium release channel) triggers muscle contraction
. The active protein is not highly structured, more than 50% of it adopting a random coil conformation. When calcium binds there is a structural change whereby the alpha-helical
content of the protein increases from 3 to 11%. Both forms of calsequestrin are phosphorylated
by casein kinase
II, but the cardiac form is phosphorylated
more rapidly and to a higher degree.
Calcium-binding protein
Calcium-binding proteins are proteins that participate in calcium cell signalling pathways by binding to Ca2+.The most ubiquitous Ca2+-sensing protein, found in all eukaryotic organisms including yeasts, is calmodulin....
of the sarcoplasmic reticulum. The protein helps hold calcium in the cisterna
Cisterna
A cisterna comprises a flattened membrane disk that makes up the Golgi apparatus. A typical Golgi has anywhere from 3 to 7 cisternae stacked upon each other like a stack of dinner plates, but there are usually around 6...
of the sarcoplasmic reticulum after a muscle contraction, even though the concentration of calcium in the sarcoplasmic reticulum is much higher than in the cytosol. It also helps the sarcoplasmic reticulum store an extraordinarily high amount of calcium ions. Each molecule of calsequestrin can bind 18 to 50 Ca2+ ions. Sequence
Sequence (biology)
A sequence in biology is the one-dimensional ordering of monomers, covalently linked within in a biopolymer; it is also referred to as the primary structure of the biological macromolecule.-See also:* Protein sequence* DNA sequence...
analysis has suggested that calcium is not bound in distinct pockets via EF-hand motifs, but rather via presentation of a charged protein surface. Two forms of calsequestrin have been identified. The cardiac form (Calsequestrin-2/CASQ2) is present in cardiac and slow skeletal muscle and the fast skeletal form (Calsequestrin-1/CASQ1) is found in fast skeletal muscle. The release of calsequestrin-bound calcium (through a a calcium release channel) triggers muscle contraction
Muscle contraction
Muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same...
. The active protein is not highly structured, more than 50% of it adopting a random coil conformation. When calcium binds there is a structural change whereby the alpha-helical
Alpha helix
A common motif in the secondary structure of proteins, the alpha helix is a right-handed coiled or spiral conformation, in which every backbone N-H group donates a hydrogen bond to the backbone C=O group of the amino acid four residues earlier...
content of the protein increases from 3 to 11%. Both forms of calsequestrin are phosphorylated
Phosphorylation
Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....
by casein kinase
Casein kinase
Casein kinase is a kinase enzyme.* Casein kinase 1* Casein kinase 2...
II, but the cardiac form is phosphorylated
Phosphorylation
Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....
more rapidly and to a higher degree.