CABP2 IS A RAT HOMOLOG OF ERP72 WITH PROTEINDISULFIDE ISOMERASE ACTIVITY

Ca-binding protein 2 (CaBP2) has been described previously as an intra cisternal calcium-binding microsomal glycoprotein [1]. We report now t he primary sequence of this protein as deduced from the corresponding cDNA. The protein possesses a C-terminal -KEEL retention sequence and three repeats of the thioredoxin-like motive -EFYAPNCGHCK-, and repres ents the rat homolog of ERp72 [2]. In contrast to earlier reports on E Rp72, CaBP2 possesses significant proteindisulfide isomerase activity. Furthermore, in contrast to ERp72, CaBP2 is a glycoporotein containin g O-linked glycans. The amount of CaBP2 in H-35 Reuber hepatoma cells increases in parallel with that of immunoglobin heavy-chain-binding pr otein under conditions which lead to impaired glycosylation, while the amount of calreticulin, another KDEL-containing glycoprotein, remains almost unchanged.