PDI family, MPD1-like subfamily; composed of eukaryotic proteins similar to Saccharomyces cerevisiae MPD1 protein, which contains a single redox active TRX domain located at the N-terminus, and an ER retention signal at the C-terminus indicative of an ER-resident protein. MPD1 has been shown to suppress the maturation defect of carboxypeptidase Y caused by deletion of the yeast PDI1 gene. Other characterized members of this subfamily include the Aspergillus niger prpA protein and Giardia PDI-1. PrpA is non-essential to strain viability, however, its transcript level is induced by heterologous protein expression suggesting a possible role in oxidative protein folding during high protein production. Giardia PDI-1 has the ability to refold scrambled RNase and exhibits transglutaminase activity.
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