Active site mutations in yeast protein disulfide isomerase cause dithiothreitol sensitivity and a reduced rate of protein folding in the endoplasmic reticulum

TY - JOUR

T1 - Active site mutations in yeast protein disulfide isomerase cause dithiothreitol sensitivity and a reduced rate of protein folding in the endoplasmic reticulum

AU - Holst, Bjørn

AU - Tachibana, Christine

AU - Winther, Jakob R.

PY - 1997

Y1 - 1997

N2 - Aspects of protein disulfide isomerase (PDI) function have been studied in yeast in vivo. PDI contains two thioredoxin-like domains, a and a', each of which contains an active-site CXXC motif. The relative importance of the two domains was analyzed by rendering each one inactive by mutation to SGAS. Such mutations had no significant effect on growth. The domains however, were not equivalent since the rate of folding of carboxypeptidase Y (CPY) in vivo was reduced by inactivation of the a domain but not the a' domain. To investigate the relevance of PDI redox potential, the G and H positions of each CGHC active site were randomly mutagenized. The resulting mutant PDIs were ranked by their growth phenotype on medium containing increasing concentrations of DTT. The rate of CPY folding in the mutants showed the same ranking as the DTT sensitivity, suggesting that the oxidative power of PDI is an important factor in folding in vivo. Mutants with a PDI that cannot perform oxidation reactions on its own (CGHS) had a strongly reduced growth rate. The growth rates, however, did not correlate with CPY folding, suggesting that the protein(s) required for optimal growth are dependent on PDI for oxidation. pdi1-deleted strains overexpressing the yeast PDI homologue EUG1 are viable. Exchanging the wild-type Eug1p C(L/I)HS active site sequences for C(L/I)HC increased the growth rate significantly, however, further highlighting the importance of the oxidizing function for optimal growth.

AB - Aspects of protein disulfide isomerase (PDI) function have been studied in yeast in vivo. PDI contains two thioredoxin-like domains, a and a', each of which contains an active-site CXXC motif. The relative importance of the two domains was analyzed by rendering each one inactive by mutation to SGAS. Such mutations had no significant effect on growth. The domains however, were not equivalent since the rate of folding of carboxypeptidase Y (CPY) in vivo was reduced by inactivation of the a domain but not the a' domain. To investigate the relevance of PDI redox potential, the G and H positions of each CGHC active site were randomly mutagenized. The resulting mutant PDIs were ranked by their growth phenotype on medium containing increasing concentrations of DTT. The rate of CPY folding in the mutants showed the same ranking as the DTT sensitivity, suggesting that the oxidative power of PDI is an important factor in folding in vivo. Mutants with a PDI that cannot perform oxidation reactions on its own (CGHS) had a strongly reduced growth rate. The growth rates, however, did not correlate with CPY folding, suggesting that the protein(s) required for optimal growth are dependent on PDI for oxidation. pdi1-deleted strains overexpressing the yeast PDI homologue EUG1 are viable. Exchanging the wild-type Eug1p C(L/I)HS active site sequences for C(L/I)HC increased the growth rate significantly, however, further highlighting the importance of the oxidizing function for optimal growth.

KW - Binding Sites

KW - Dithiothreitol

KW - Endoplasmic Reticulum

KW - Escherichia coli

KW - Fungal Proteins

KW - Glycosylation

KW - Isomerases

KW - Mutagenesis

KW - Oxidation-Reduction

KW - Protein Disulfide-Isomerases

KW - Protein Folding

KW - Protein Structure, Tertiary

KW - Saccharomyces cerevisiae

KW - Saccharomyces cerevisiae Proteins

KW - Sulfhydryl Reagents

KW - Thioredoxins

M3 - Journal article

C2 - 9298979

SN - 0021-9525

VL - 138

SP - 1229

EP - 1238

JO - Journal of Cell Biology

JF - Journal of Cell Biology

IS - 6

ER -