DICTYOSTELIUM-DISCOIDEUM PROTEIN DISULFIDE-ISOMERASE, AN ENDOPLASMIC-RETICULUM RESIDENT ENZYME LACKING A KDEL-TYPE RETRIEVAL SIGNAL

The primary activity of protein disulfide isomerase (PDI), a multifunc tional resident of the endoplasmic reticulum (ER), is the isomerizatio n of disulfide bridges during protein folding, We isolated a cDNA enco ding Dictyostelium discoideum PDI (Dp-PDI). Phylogenetic analyses and basic biochemical properties indicate that it belongs to a subfamily c alled P5, many members of which differ from the classical PDIs in many respects, They lack an intervening inactive thioredoxin module, a C-t erminal acidic domain involved in Ca2+ binding and a KDEL-type retriev al signal, Despite the absence of this motif, the ER is the steady-sta te location of Dd-PDI, suggesting the existence of an alternative rete ntion mechanism for PS-related enzymes. (C) 1997 Federation of Europea n Biochemical Societies.