Calreticulin: one protein, one gene, many functions

The endoplasmic reticulum (ER) plays a critical role in the synthesis and c haperoning of membrane-associated and secreted proteins. The membrane is al so an important site of Ca2+ storage and release. Calreticulin is a unique ER luminal resident protein. The protein affects many cellular functions, b oth in the ER lumen and outside of the ER environment. In the ER lumen, cal reticulin performs two major functions: chaperoning and regulation of Ca2homoeostasis. Calreticulin is a highly versatile lectin-like chaperone, and it participates during the synthesis of a variety of molecules, including ion channels, surface receptors, integrins and transporters. The protein al so affects intracellular Ca2+ homoeostasis by modulation of ER Ca2+ storage and transport. Studies on the cell biology of calreticulin revealed that t he ER membrane is a very dynamic intracellular compartment affecting many a spects of cell physiology.