Calreticulin

Calreticulin is a calcium-dependent ER chaperone, involved in protein folding, maturation, and cellular localization. Calreticulin is a highly conserved 48 kDa protein encoded by the CALR gene. Calreticulin and its homolog calnexin regulate the folding and degradation of newly synthesized glycoproteins as they are translocated into the ER (1). Misfolded proteins recognized by calreticulin are targeted to the ER-associated degradation (ERAD) pathway. Within the ER, calreticulin also plays an important role in calcium homeostasis.

Calnexin is an abundant 90kDa chaperone protein that resides in the membrane of the endoplasmic reticulum. Calnexin and the related calreticulin protein function together to ensure the proper folding of glycoproteins. By binding to partially folded or misfolded proteins, Calnexin functions as an important quality control monitor ensuring proper folding of proteins destined for the plasma membrane or secretion.

Calreticulin is a Calcium binding chaperone that has multiple functions both inside and outside the endoplasmic reticulum. Calreticulin is involved in the quality control of newly synthesized proteins and glycoproteins, interacting with various other ER chaperones, specifically Calnexin.