Functional Differences in Yeast Protein Disulfide Isomerases

Abstract

PDI1 is the essential gene encoding protein disulfide isomerase in yeast. The Saccharomyces cerevisiae genome, however, contains four other nonessential genes with homology to PDI1: MPD1, MPD2, EUG1, and EPS1. We have investigated the effects of simultaneous deletions of these genes. In several cases, we found that the ability of the PDI1 homologues to restore viability to a pdi1-deleted strain when overexpressed was dependent on the presence of low endogenous levels of one or more of the other homologues. This shows that the homologues are not functionally interchangeable. In fact, Mpd1p was the only homologue capable of carrying out all the essential functions of Pdi1p. Furthermore, the presence of endogenous homologues with a CXXC motif in the thioredoxin-like domain is required for suppression of a pdi1 deletion by EUG1 (which contains two CXXS active site motifs). This underlines the essentiality of protein disulfide isomerase-catalyzed oxidation. Most mutant combinations show defects in carboxypeptidase Y folding as well as in glycan modification. There are, however, no significant effects on ER-associated protein degradation in the various protein disulfide isomerase-deleted strains.

Domain Architecture of Protein-disulfide Isomerase Facilitates Its Dual Role as an Oxidase and an Isomerase in Ero1p-mediated Disulfide Formation

“…However, we found that the substrate-binding domain (BЈ) was not required for productive interaction with Ero1p. We also found that Ero1p is fairly nonspecific in its recognition of thioredoxin domains, which helps explain why the expression of several PDI homologs can rescue the viability of a ⌬pdi1 strain (11,12,37). This lack of discrimination seems at odds with the strong preference that Ero1p has for thioredoxin domains over unfolded proteins (19).…”

Biology of the Heat Shock Response and Protein Chaperones: Budding Yeast (Saccharomyces cerevisiae) as a Model System

“…All are soluble lumenal proteins, except for Eps1, which is the only membrane-associated PDI1 homolog. Evidence from different groups showed that the overexpression of any of these homologs can partially suppress the lethality of the pdi1⌬ strain, suggesting that they have the ability to carry out the minimum Pdi1 function required for cell survival (324). Why, then, is the deletion of PDI1 lethal?…”

“…Interestingly, this construct was able to rescue a pdi1⌬ eug1⌬ mpd1⌬ mpd2⌬ eps1⌬ strain, suggesting that low PDI levels are sufficient for viability. Moreover, of all the PDI genes, only MPD1 and PDI1 are competent to serve as the sole source of PDI enzyme activity (324). A series of genetic and biochemical experiments suggested that Mpd1 and Mpd2 perform complementary functions.…”

Distinct Roles of Protein Disulfide Isomerase and P5 Sulfhydryl Oxidoreductases in Multiple Pathways for Oxidation of Structurally Diverse Storage Proteins in Rice

“…The essential function and broad substrate specificity of the PDI family oxidoreductases complicate the identification of redundant and specific functions of each member of the PDI family in vivo. Yeast Pdi1p is essential for cell viability, but the functions of Pdi1p can be performed by other PDI family oxidoreductases, such as Mpd1p, when overexpressed (Tachikawa et al, 1995;Nørgaard et al, 2001). In human, extensive studies have elucidated some specific functions of the PDI family oxidoreductases in different cells.…”