Conversely, membrane-anchored calreticulin bound to a similar set of glycoproteins as calnexin. However, when calnexin was expressed as a soluble protein in L cells, the pattern of associated glycoproteins changed to resemble that of calreticulin. We also determined that a soluble form of calnexin (residues 1-387) can functionally replace its membrane-bound counterpart. Indeed, the functions of calnexin and calreticulin were largely interchangeable.
Using a Drosophila expression system and the mouse class I histocompatibility molecule as a model glycoprotein, we found that calreticulin does possess apparent chaperone and quality control functions, enhancing class I folding and subunit assembly, stabilizing subunits, and impeding export of assembly intermediates from the ER. Calreticulin, a soluble analog of calnexin, is thought to possess similar functions, but these have not been directly demonstrated in vivo. Although many glycoproteins bind to both calnexin and calreticulin, there are differences in the spectrum of glycoproteins that each binds. Calnexin is a membrane protein of the endoplasmic reticulum (ER) that functions as a The general concept of molecular chaperones - PubMed and as a component of the ER quality control machinery. Both proteins contain a lectin site that directs their association with newly synthesized glycoproteins. Calnexin is a membrane protein of the endoplasmic reticulum (ER) that functions as a molecular chaperone and as a component of the ER quality control machinery.
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