Mutational analysis of calnexin

Abstract

Calnexin is a type I endoplasmic reticulum lectin-like chaperone protein. In this study, we have used site-specific mutagenesis to investigate the functional importance of glutamate E351 found at the tip of the P-domain of calnexin, and tryptophan W428 found in the carbohydrate binding region of the globular domain of the protein. The E351 and W428 calnexin mutants lost the ability to inhibit aggregation of IgY (glycosylated substrate). The E351 mutation led to slightly enhanced ERp57 binding to calnexin, whereas W428 greatly enhanced binding of ERp57 to calnexin. These findings indicate that modification of a residue(s) in the carbohydrate binding region may have a profound effect on the structural and functional properties of the P-domain and consequently on association of calnexin with the folding enzyme ERp57.