OVERPRODUCTION OF MPD2P SUPPRESSES THE LETHALITY OF PROTEIN DISULFIDE-ISOMERASE DEPLETION IN A CXXC SEQUENCE-DEPENDENT MANNER

The third multicopy suppressor gene of the PDI1 deletion from Saccharo myces cerevisiae, MPD2, was isolated and characterized, The MPD2 gene encodes a protein with a putative signal sequence, ER retention signal , and a disulfide isomerase active site Like sequence, The amino acid sequence around the active site like sequence is similar to the thiore doxin-like domains of PDI and PDI related proteins, although the simil arity is comparatively low. A Delta-pdi1 strain overproducing Mpd2p sh owed slow growth and was sensitive to 1 mM dithiothreitol. Mpd2p can b e detected in wild type cells and is a glycoprotein. Although the MPD2 gene was not essential for growth, overexpression of the gene partial ly restored the maturation defect of carboxypeptidase Y caused by the PDI1 deletion. Mutagenesis analysis revealed that Mpd2p can compensate for the loss of PDI with its CXXC sequence. (C) 1997 Academic Press.