The gene for calreticulin (CALR) is located on the human chromosome 19p13.13. The encoded protein is a predominantly conserved calcium-binding chaperone, which is localized primarily to the lumen of the endoplasmic reticulum (ER). Calreticulin comprises three domains, a globular N-domain, a proline-rich P-domain, and a highly acidic C-domain.
Calreticulin facilitates transient interaction with newly synthesized cellular and extracellular proteins for folding and assembling in the endoplasmic reticulum (ER) before its localization to the cytosol or cell surface. Calreticulin acts as a lectin-like chaperone binding oligosaccharide residues of newly synthesized N-linked glycoproteins and misfolded proteins. It is believed to play a critical role in quality control processes during protein synthesis and folding and calcium (Ca2+) homeostasis. Increased expression of calreticulin increases the Ca2+ storage capacity of the ER. It also appears to modulate store-operated Ca2+-influx and to alter Ca2+ transport by the sarcoplasmic/ER Ca2+-adenosine triphosphatase (ATPase) (SERCA). Overexpression of calreticulin results in increased sensitivity of HeLa cells to drug-induced apoptosis. However, increased resistance to apoptosis has been observed in calreticulin-deficient cells.
