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.