Identification of calnexin as a binding protein for Amadori-modified glycated albumin

Albumin modified by Amadori glucose adducts (glycated albumin) selectively binds to glomerular mesangial cells and triggers signal transduction proces ses that modulate cellular function. To identify glycated albumin binding p roteins, we applied membrane extracts prepared from murine mesangial cells to a column of lysine-Sepharose followed by application to an affinity colu mn of fructosyllysine-Sepharose. This procedure yielded an approximately 90 kDa polypeptide that immunoreacted with Amadori-modified but not carbohydr ate-free albumin. MALDI mass fingerprinting matched 9 out of 25 peptides wi th calnexin, and amino acid analysis showed homology with this transmembran e calcium-binding protein of the calreticulin family. These results indicat e that one of the mesangial cell receptors for glycated albumin is a calnex in-like protein. (C) 2001 Academic Press.