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Functional differences in yeast protein disulfide isomerases.

Nørgaard P, Westphal V, Tachibana C, Alsøe L, Holst B, Winther JR - J. Cell Biol. (2001)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Yeast Genetics, Carlsberg Laboratory, DK-2500 Copenhagen Valby, Denmark.

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.

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Yeast contains three genes that encode soluble ER proteins with sequence homology to Pdi1p. Open boxes indicate the position and extent of thioredoxin-like domains. Active-site cysteines and the amino acid residues between them are shown. The protein Eug1p has ∼40% sequence identity to Pdi1p and contains, like Pdi1p, two regions with sequence homology to thioredoxin. MPD1 and MPD2 encode proteins that are smaller than Pdi1p and Eug1p and contain only one thioredoxin-like active site. The protein Eps1p contains one thioredoxin-like region as well as a transmembrane domain (the closed box marked TMD).
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Figure 1: Yeast contains three genes that encode soluble ER proteins with sequence homology to Pdi1p. Open boxes indicate the position and extent of thioredoxin-like domains. Active-site cysteines and the amino acid residues between them are shown. The protein Eug1p has ∼40% sequence identity to Pdi1p and contains, like Pdi1p, two regions with sequence homology to thioredoxin. MPD1 and MPD2 encode proteins that are smaller than Pdi1p and Eug1p and contain only one thioredoxin-like active site. The protein Eps1p contains one thioredoxin-like region as well as a transmembrane domain (the closed box marked TMD).

Mentions: In Saccharomyces cerevisiae, the complete genome sequence shows that the number of putative PDIs is most likely limited to five, of which the PDI1 gene is the only essential gene (Farquhar et al. 1991). Overexpression of any of the nonessential homologues EUG1, MPD1, MPD2, or EPS1, however, has been found to suppress the lethality caused by deletion of PDI1 (Tachibana and Stevens 1992; Tachikawa et al. 1995, Tachikawa et al. 1997; Wang and Chang 1999). Eug1p shows an overall sequence identity of ∼40% to Pdi1p and contains two thioredoxin-like domains (Fig. 1). Unlike all known PDIs, the active sites of Eug1p have a CXXS motif (Tachibana and Stevens 1992). Thus, the active sites of Eug1p are not able to form intramolecular disulfide bonds. Therefore, Eug1p alone is unable to carry oxidizing equivalents. MPD1 and MPD2 encode proteins containing only a single thioredoxin-like domain (Fig. 1). Apart from the thioredoxin domain, they share no further sequence homology with any protein of known function. Overexpression of EUG1, MPD1, or MPD2 does not fully complement a pdi1 deletion since such strains show a reduced folding rate of procarboxypeptidase Y (proCPY) (Tachibana and Stevens 1992; Tachikawa et al. 1995, Tachikawa et al. 1997).


Functional differences in yeast protein disulfide isomerases.

Nørgaard P, Westphal V, Tachibana C, Alsøe L, Holst B, Winther JR - J. Cell Biol. (2001)

Yeast contains three genes that encode soluble ER proteins with sequence homology to Pdi1p. Open boxes indicate the position and extent of thioredoxin-like domains. Active-site cysteines and the amino acid residues between them are shown. The protein Eug1p has ∼40% sequence identity to Pdi1p and contains, like Pdi1p, two regions with sequence homology to thioredoxin. MPD1 and MPD2 encode proteins that are smaller than Pdi1p and Eug1p and contain only one thioredoxin-like active site. The protein Eps1p contains one thioredoxin-like region as well as a transmembrane domain (the closed box marked TMD).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2195995&req=5

Figure 1: Yeast contains three genes that encode soluble ER proteins with sequence homology to Pdi1p. Open boxes indicate the position and extent of thioredoxin-like domains. Active-site cysteines and the amino acid residues between them are shown. The protein Eug1p has ∼40% sequence identity to Pdi1p and contains, like Pdi1p, two regions with sequence homology to thioredoxin. MPD1 and MPD2 encode proteins that are smaller than Pdi1p and Eug1p and contain only one thioredoxin-like active site. The protein Eps1p contains one thioredoxin-like region as well as a transmembrane domain (the closed box marked TMD).
Mentions: In Saccharomyces cerevisiae, the complete genome sequence shows that the number of putative PDIs is most likely limited to five, of which the PDI1 gene is the only essential gene (Farquhar et al. 1991). Overexpression of any of the nonessential homologues EUG1, MPD1, MPD2, or EPS1, however, has been found to suppress the lethality caused by deletion of PDI1 (Tachibana and Stevens 1992; Tachikawa et al. 1995, Tachikawa et al. 1997; Wang and Chang 1999). Eug1p shows an overall sequence identity of ∼40% to Pdi1p and contains two thioredoxin-like domains (Fig. 1). Unlike all known PDIs, the active sites of Eug1p have a CXXS motif (Tachibana and Stevens 1992). Thus, the active sites of Eug1p are not able to form intramolecular disulfide bonds. Therefore, Eug1p alone is unable to carry oxidizing equivalents. MPD1 and MPD2 encode proteins containing only a single thioredoxin-like domain (Fig. 1). Apart from the thioredoxin domain, they share no further sequence homology with any protein of known function. Overexpression of EUG1, MPD1, or MPD2 does not fully complement a pdi1 deletion since such strains show a reduced folding rate of procarboxypeptidase Y (proCPY) (Tachibana and Stevens 1992; Tachikawa et al. 1995, Tachikawa et al. 1997).

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Yeast Genetics, Carlsberg Laboratory, DK-2500 Copenhagen Valby, Denmark.

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.

Show MeSH
Related in: MedlinePlus