Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P11021 (BiP)
 2,049 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The C-terminal region of the chaperone-like pro-sequence (py) of yeast carboxypeptidase Y (CPY) is suggested to be crucial for the folding of mature CPY. In order to study the influence of hydrophobic residues in this domain, a set of mutations have been introduced in py. Unexpectedly, only small amounts of CPY precursors are expressed when Leu108, at the C-terminal end of py, is substituted for polar residues Lys, Arg or Asp. In contrast, substitution with hydrophobic residues Val, Ile or Ala permit normal expression. Interestingly, the poorly expressed molecules are coreglycosylated, implying that they have failed to leave the endoplasmic reticulum (ER). The ER-retained molecules caused an induction in the levels of BiP, signifying that polar substitutions at position 108 of pre-py-CPY induce misfolding. Quite surprisingly, a reporter gene, linked to concatamerized unfolded-protein-response elements, reveals that py-mediated misfolding of CPY is not really identical in all mutants. This shows that a simple transcriptional assay can assess the subtleties of pro-sequence mediated protein folding in an eukaryotic cell.
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PMID:The unfolded-protein-response element discriminates misfolding induced by different mutant pro-sequences of yeast carboxypeptidase Y. 772 51

Proteins enter the secretory pathway through the endoplasmic reticulum, which delivers properly folded proteins to their site of action and contains a quality-control system to monitor and prevent abnormal proteins from being delivered. Many of these proteins are degraded by the cytoplasmic proteasome, which requires their retrograde transport to the cytoplasm. Based on a co-immunoprecipitation of major histocompatibility complex (MHC) class I heavy-chain breakdown intermediates with the translocon subunit Sec61p, it was speculated that Sec61p maybe involved in retrograde transport. Here we present functional evidence from genetic studies that Sec61p mediates retrograde transport of a mutated lumenal yeast carboxypeptidase ycsY (CPY*) in vivo. The endoplasmic reticulum lumenal chaperone BiP (Kar2p) and Sec63p, which are also subunits of the import machinery, are involved in export of CPY* to the cytosol. Thus our results demonstrate that retrograde transport of proteins is mediated by a functional translocon. We consider the export of endoplasmic reticulum-localized proteins to the cytosol by the translocon for proteasome degradation to be a general process in eukaryotic cell biology.
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PMID:Mutant analysis links the translocon and BiP to retrograde protein transport for ER degradation. 927 52

To study the degradation requirements of unassembled immunoglobulin (Ig) chains, we heterologously expressed a cDNA encoding the secretory form of murine mu in the yeast S. cerevisiae. We found that mu chains were translocated into and retained in the endoplasmic reticulum (ER) as they were N-glycosylated and bound to the yeast homolog of BiP, Kar2p. Similar to mutant yeast carboxypeptidase Y (CPY*), known to undergo cytosolic degradation, mu protein is stabilized in yeast mutants lacking the ubiquitinating enzymes Ubc6p and Ubc7p or in cells overexpressing mutant ubiquitin. Unexpectedly, the translation inhibitor cycloheximide (CHX), but not puromycin, led to the accumulation of polyubiquitinated mu chains that were still glycosylated. By contrast, degradation of CPY* was not impaired by CHX, indicating that the drug affects a substrate-specific degradation step. In contrast to the situation for CPY*, the ER-transmembrane protein Der1p is not essential for mu degradation. Strikingly, however, the CHX-induced accumulation of polyubiquitinated Igmu chains was stronger in deltader1-mutants as compared to wild-type cells, indicating an additive effect of two inhibitory conditions. The results support a previously unknown activity of CHX, i.e. impairing the degradation of transport-incompetent secretory mu chains. Moreover, this activity will allow to dissect substrate-specific steps in ER associated protein degradation.
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PMID:Cycloheximide, a new tool to dissect specific steps in ER-associated degradation of different substrates. 1043 31