Identification and crystallization of a protease-resistant core of calnexin that retains biological activity

Calnexin is a molecular chaperone that facilitates folding of glycoproteins in the endoplasmic reticulum (ER). The cloned lumenal domain of canine cal nexin, cnx Delta TMC, retains its biological activity without the transmemb rane and cytosolic region. For the purpose of structure determination we ge nerated a crystallizable core by mild proteolysis and identified its termin i by N-terminal sequencing and molecular mass determination. A truncated ge ne was cloned accordingly. Its product, cnx Delta N25C15, was purified to a pparent homogeneity and crystallized. This truncated variant remains biolog ically active as shown by its binding to monoglucosylated oligosaccharides and functional interaction with ERp57. A heavy atom derivative was identifi ed. (C) 1998 Academic Press.