PROTEIN DISULFIDE-ISOMERASE ASSOCIATES WITH MISFOLDED HUMAN LYSOZYME IN-VIVO

Wild-type human lysozyme (hLZM) is quantitatively secreted into the me dia when expressed in mouse fibroblast cells, but some misfolded hLZMs are retained and rapidly degraded in a pre-Golgi compartment (Omura, F., Otsu, M., Yoshimori, T., Tashiro, Y., and Kikuchi, M. (1992) Eur. J. Biochem. 210, 591-599). To detect the association with misfolded hL ZMs of cellular proteins involved in their folding, retention, and pre -Golgi degradation, a co-precipitation experiment was carried out usin g anti-hLZM antibody and metabolically labeled cell lysates, which wer e treated with a membrane-permeable cross-linking reagent. Here we rep ort that protein disulfide isomerase associated in vivo with misfolded hLZMs, but not with the wild-type protein, and discuss the possible r ole of protein disulfide isomerase in the quality control of newly syn thesized proteins in the endoplasmic reticulum.