Calsequestrin calcium binding

Calpactins calectrin Calpain Calsequestrin Membrane-binding proteins (365) Protease controlling cell adhesion (366) Sequesters calcium within the sarcoplasmic reticulum when muscles relax (80,367)... 

ATP is used not only to power muscle contraction, but also to re-establish the resting state of the cell. At the end of the contraction cycle, calcium must be transported back into the sarcoplasmic reticulum, a process which is ATP driven by an active pump mechanism. Additionally, an active sodium-potassium ATPase pump is required to reset the membrane potential by extruding sodium from the sarcoplasm after each wave of depolarization. When cytoplasmic Ca2- falls, tropomyosin takes up its original position on the actin and prevents myosin binding and the muscle relaxes. Once back in the sarcoplasmic reticulum, calcium binds with a protein called calsequestrin, where it remains until the muscle is again stimulated by a neural impulse leading to calcium release into the cytosol and the cycle repeats. 

Calsequestrin is a calcium-storage protein found in the sacroplasmic reticulum, which binds about 50 calcium ions per monomer (molecular weight 40 000) with binding constants in the range 103-105 dm3 mol. Release and uptake of Ca2+ during muscle contradion and relaxation involve this store. Calsequestrin from rabbit skeletal muscle has a random coil conformation in the absence of calcium. Binding of Ca2+ is associated with a change to a more compact structure.267... 

Culligan, K., Banville, N., Dowling, P., and Ohlendieck, K., 2002, Drastic reduction of calsequestrin-like proteins and impaired calcium binding in dystrophic mdx muscle, J Appl Physiol, 92, pp 435 145. 

The last calcium binding protein to be discussed in the miscellaneous category is calsequestrin. This protein was isolated from the lumen of the sarcoplasmic reticulum and because of the high binding capacity, has been suggested to be a major site of calcium binding in the interior of the sarcoplasmic reticulum. 

Relaxation of the muscle is brought about by removal of the ionic calcium from the sarcoplasm. This calcium is transported across the membrane of the sarcoplasmic reticulum, in an energy requiring process. In addition to the calcium pumping ATPase, the sarcoplasmic reticulum also contains a calcium binding protein called calsequestrin (Section 4.3.3). Some of the calcium segregated by the sarcoplasmic reticulum is apparently bound to this protein within the lumen of the sarcoplasmic reticulum. As sequestration of calcium ions into sarcoplasmic reticulum proceeds, more calcium ions dissociate from their binding sites on troponin C, re-... 

The localization of the IP, receptor has been compared to the localization of other luminal or membrane components of the endoplasmatic reticulum related to Ca "" homeostasis. The membrane pump Ca -ATPase, immunolabelled with antibodies against cardiac Ca -ATPase, was found to be located in regular cisternae of the endoplasmatic reticulum, the lateral tips of cisternae of the Golgi complex and in calciosomes of Purkinje cells (Kaprielian, 1989 Michelangeli et al., 1991 Villa et al., 1991 Takei et al., 1992) (Fig. 27). Distal axons of Purkinje cells, however, lacked Ca "-ATPase im-munoreactivity (Takei et al., 1992). Appreciable levels of calsequestrin, the main intraluminal calcium-binding protein of muscle, were present in Purkinje cells of the chicken. Calsequestrin-immunoreactivity was present over the lumen (Villa et al., 1991) and membranes (Takei et al., 1992) of stacked and isolated cisternae of the endoplasmatic reticulum and in a subpopulation of calciosomes (Volpe et al., 1988 Volpe and Villa,... 

Campbell, K. R MacLennan, D. H. Jorgensen, A. O. Staining of the calcium-binding proteins, calsequestrin, calmodulin, troponin C, and S-100, with the cationic carbocyanine dye Stains-aU . J. Biol. Chem. 1983, 258, 11267-11273. 

Somlyo Regarding the nuclear envelope and Ca2+, there is an old picture in a book showing strontium in the nuclear envelope within the perinuclear space (Somlyo Somlyo 1975). The trouble is, when we load with calcium oxalate, we can get an egg shell of calcium oxalate around the nucleus, but when we do electron probe analysis under normal physiological conditions, there doesn t seem to be detectable Ca2+ in the nuclear space. However, this is probably because there is no calsequestrin or other Ca2+ binding protein present. 

Another group of calcium-buffering and storage proteins with remarkable Ca2+-binding properties are the 40- to 45-kDa calsequestrins, which are found in the lumen of the ER (sarcoplasmic reticulum) of skeletal muscle. Calsequestrins are not typical EF-hand proteins but have a high content of glutamate and aspartate. They bind 50 Ca2+ per molecule of protein with Kd 1 mM.104 105 Similar proteins called calreticulins are found in most non-muscle cells.106 107... 

The identity of two other reported binding proteins from sarcoplasmic reticulum is in doubt. Tropocalcin, isolated by Benson and Han may be identical to calsequestrin (78) and cardioglobulin-C (79) may be identical to the calcium transport ATPase (80), although the cardioglobulin has also been demonstrated in blood plasma (79). 

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