scholarly journals O-Mannosylation Protects Mutant Alpha-Factor Precursor from Endoplasmic Reticulum-associated Degradation

2001 ◽  
Vol 12 (4) ◽  
pp. 1093-1101 ◽  
Author(s):  
Carol Harty ◽  
Sabine Strahl ◽  
Karin Römisch
Keyword(s):  
Endoplasmic Reticulum ◽  
Yeast Cells ◽  
Misfolded Proteins ◽  
Secretory Proteins ◽  
Wild Type ◽  
Folding Intermediates ◽  
Alpha Factor ◽  
Er Export ◽  
Sec61 Channel

Secretory proteins that fail to fold in the endoplasmic reticulum (ER) are transported back to the cytosol and degraded by proteasomes. It remains unclear how the cell distinguishes between folding intermediates and misfolded proteins. We asked whether misfolded secretory proteins are covalently modified in the ER before export. We found that a fraction of mutant alpha-factor precursor, but not the wild type, was progressively O-mannosylated in microsomes and in intact yeast cells by proteinO-mannosyl transferase 2 (Pmt2p).O-Mannosylation increased significantly in vitro under ER export conditions, i.e., in the presence of ATP and cytosol, and this required export-proficient Sec61p in the ER membrane. Deletion ofPMT2, however, did not abrogate mutant alpha-factor precursor degradation but, rather, enhanced its turnover in intact yeast cells. In vitro, O-mannosylated mutant alpha-factor precursor was stable and protease protected, and a fraction was associated with Sec61p in the ER lumen. Thus, prolonged ER residence allows modification of exposed O-mannosyl acceptor sites in misfolded proteins, which abrogates misfolded protein export from the ER at a posttargeting stage. We conclude that there is a limited window of time during which misfolded proteins can be removed from the ER before they acquire inappropriate modifications that can interfere with disposal through the Sec61 channel.

Sec59 encodes a membrane protein required for core glycosylation in Saccharomyces cerevisiae

1989 ◽  
Vol 9 (3) ◽  
pp. 1191-1199
Author(s):  
M Bernstein ◽  
F Kepes ◽  
R Schekman
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Protein Product ◽  
Carboxypeptidase Y ◽  
Secretory Proteins ◽  
Restrictive Temperature ◽  
Wild Type ◽  
Partial Restoration ◽  
Alpha Factor ◽  
Mutant Cells

When incubated at a restrictive temperature, Saccharomyces cerevisiae sec59 mutant cells accumulate inactive and incompletely glycosylated forms of secretory proteins. Three different secretory polypeptides (invertase, pro-alpha-factor, and pro-carboxypeptidase Y) accumulated within a membrane-bounded organelle, presumably the endoplasmic reticulum, and resisted proteolytic degradation unless the membrane was permeabilized with detergent. Molecular cloning and DNA sequence analysis of the SEC59 gene predicted an extremely hydrophobic protein product of 59 kilodaltons. This prediction was confirmed by reconstitution of the sec59 defect in vitro. The alpha-factor precursor, which was translated in a soluble fraction from wild-type cells, was translocated into, but inefficiently glycosylated within, membranes from sec59 mutant cells. Residual glycosylation activity of membranes of sec59 cells was thermolabile compared with the activity of wild-type membranes. Partial restoration of glycosylation was obtained in reactions that were supplemented with mannose or GDP-mannose, but not those supplemented with other sugar nucleotides. These results were consistent with a role for the Sec59 protein in the transfer of mannose to dolichol-linked oligosaccharide.

scholarly journals Sec59 encodes a membrane protein required for core glycosylation in Saccharomyces cerevisiae.

1989 ◽  
Vol 9 (3) ◽  
pp. 1191-1199 ◽  
Author(s):  
M Bernstein ◽  
F Kepes ◽  
R Schekman
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Protein Product ◽  
Carboxypeptidase Y ◽  
Secretory Proteins ◽  
Restrictive Temperature ◽  
Wild Type ◽  
Partial Restoration ◽  
Alpha Factor ◽  
Mutant Cells

When incubated at a restrictive temperature, Saccharomyces cerevisiae sec59 mutant cells accumulate inactive and incompletely glycosylated forms of secretory proteins. Three different secretory polypeptides (invertase, pro-alpha-factor, and pro-carboxypeptidase Y) accumulated within a membrane-bounded organelle, presumably the endoplasmic reticulum, and resisted proteolytic degradation unless the membrane was permeabilized with detergent. Molecular cloning and DNA sequence analysis of the SEC59 gene predicted an extremely hydrophobic protein product of 59 kilodaltons. This prediction was confirmed by reconstitution of the sec59 defect in vitro. The alpha-factor precursor, which was translated in a soluble fraction from wild-type cells, was translocated into, but inefficiently glycosylated within, membranes from sec59 mutant cells. Residual glycosylation activity of membranes of sec59 cells was thermolabile compared with the activity of wild-type membranes. Partial restoration of glycosylation was obtained in reactions that were supplemented with mannose or GDP-mannose, but not those supplemented with other sugar nucleotides. These results were consistent with a role for the Sec59 protein in the transfer of mannose to dolichol-linked oligosaccharide.

scholarly journals Reconstitution of protein transport from the endoplasmic reticulum to the Golgi complex in yeast: the acceptor Golgi compartment is defective in the sec23 mutant.

1988 ◽  
Vol 107 (4) ◽  
pp. 1465-1476 ◽  
Author(s):  
H Ruohola ◽  
A K Kabcenell ◽  
S Ferro-Novick
Keyword(s):  
Endoplasmic Reticulum ◽  
Secretory Pathway ◽  
Protein Transport ◽  
Yeast Cells ◽  
Restrictive Temperature ◽  
Transport Reaction ◽  
Permeabilized Cells ◽  
Alpha Factor

Using either permeabilized cells or microsomes we have reconstituted the early events of the yeast secretory pathway in vitro. In the first stage of the reaction approximately 50-70% of the prepro-alpha-factor, synthesized in a yeast translation lysate, is translocated into the endoplasmic reticulum (ER) of permeabilized yeast cells or directly into yeast microsomes. In the second stage of the reaction 48-66% of the ER form of alpha-factor (26,000 D) is then converted to the high molecular weight Golgi form in the presence of ATP, soluble factors and an acceptor membrane fraction; GTP gamma S inhibits this transport reaction. Donor, acceptor, and soluble fractions can be separated in this assay. This has enabled us to determine the defective fraction in sec23, a secretory mutant that blocks ER to Golgi transport in vivo. When fractions were prepared from mutant cells grown at the permissive or restrictive temperature and then assayed in vitro, the acceptor Golgi fraction was found to be defective.

scholarly journals Misfolded Proteins Traffic from the Endoplasmic Reticulum (ER) Due to ER Export Signals

2007 ◽  
Vol 18 (2) ◽  
pp. 455-463 ◽  
Author(s):  
Margaret M. Kincaid ◽  
Antony A. Cooper
Keyword(s):  
Endoplasmic Reticulum ◽  
Misfolded Proteins ◽  
Secretory Proteins ◽  
Therapeutic Approaches ◽  
Important Distinction ◽  
Anterograde Transport ◽  
Er Retention ◽  
Folded Proteins ◽  
Er Export ◽  
Export Signal

Most misfolded secretory proteins remain in the endoplasmic reticulum (ER) and are degraded by ER-associated degradation (ERAD). However, some misfolded proteins exit the ER and traffic to the Golgi before degradation. Using model misfolded substrates, with or without defined ER exit signals, we found misfolded proteins can depart the ER by continuing to exhibit the functional export signals present in the corresponding correctly folded proteins. Anterograde transport of misfolded proteins utilizes the same machinery responsible for exporting correctly folded proteins. Passive ER retention, in which misfolded proteins fail to exit the ER due to the absence of exit signals or the inability to functionally present them, likely contributes to the retention of nonnative proteins in the ER. Intriguingly, compromising ERAD resulted in increased anterograde trafficking of a misfolded protein with an ER exit signal, suggesting that ERAD and ER exit machinery can compete for binding of misfolded proteins. Disabling ERAD did not result in transport of an ERAD substrate lacking an export signal. This is an important distinction for those seeking possible therapeutic approaches involving inactivating ERAD in anticipation of exporting a partially active protein.

scholarly journals Membrane aberrancy and unfolded proteins activate the endoplasmic reticulum stress sensor Ire1 in different ways

2011 ◽  
Vol 22 (18) ◽  
pp. 3520-3532 ◽  
Author(s):  
Thanyarat Promlek ◽  
Yuki Ishiwata-Kimata ◽  
Masahiro Shido ◽  
Mitsuru Sakuramoto ◽  
Kenji Kohno ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Transmembrane Domain ◽  
Membrane Lipid ◽  
Yeast Cells ◽  
Wild Type ◽  
Unfolded Proteins ◽  
Unfolded Protein ◽  
The Unfolded Protein Response ◽  
Protein Response

Eukaryotic cells activate the unfolded-protein response (UPR) upon endoplasmic reticulum (ER) stress, where the stress is assumed to be the accumulation of unfolded proteins in the ER. Consistent with previous in vitro studies of the ER-luminal domain of the mutant UPR initiator Ire1, our study show its association with a model unfolded protein in yeast cells. An Ire1 luminal domain mutation that compromises Ire1's unfolded-protein–associating ability weakens its ability to respond to stress stimuli, likely resulting in the accumulation of unfolded proteins in the ER. In contrast, this mutant was activated like wild-type Ire1 by depletion of the membrane lipid component inositol or by deletion of genes involved in lipid homeostasis. Another Ire1 mutant lacking the authentic luminal domain was up-regulated by inositol depletion as strongly as wild-type Ire1. We therefore conclude that the cytosolic (or transmembrane) domain of Ire1 senses membrane aberrancy, while, as proposed previously, unfolded proteins accumulating in the ER interact with and activate Ire1.

scholarly journals Conversion of secretory proteins into membrane proteins by fusing with a glycosylphosphatidylinositol anchor signal of alkaline phosphatase

1994 ◽  
Vol 301 (2) ◽  
pp. 577-583 ◽  
Author(s):  
K Oda ◽  
J Cheng ◽  
T Saku ◽  
N Takami ◽  
M Sohda ◽  
...  
Keyword(s):  
Alkaline Phosphatase ◽  
Endoplasmic Reticulum ◽  
Aspartic Acid ◽  
Chimeric Protein ◽  
Attachment Site ◽  
In Vitro Translation ◽  
Placental Alkaline Phosphatase ◽  
Wild Type ◽  
Aspartic Acid Residue

Placental alkaline phosphatase (PLAP) is initially synthesized as a precursor (proPLAP) with a C-terminal extension. We constructed a recombinant cDNA which encodes a chimeric protein (alpha GL-PLAP) comprising rat alpha 2u-globulin (alpha GL) and the C-terminal extension of PLAP. Two molecular species (25 kDa and 22 kDa) were expressed in the COS-1 cell transfected with the cDNA for alpha GL-PLAP. Only the 22 kDa form was labelled with both [3H]stearic acid and [3H]ethanolamine. Upon digestion with phosphatidylinositol-specific phospholipase C the 22 kDa form was released into the medium, indicating that this form is anchored on the cell surface via glycosylphosphatidylinositol (GPI). A specific IgG raised against a C-terminal nonapeptide of proPLAP precipitated the 25 kDa form but not the 22 kDa form, suggesting that the 25 kDa form is a precursor retaining the C-terminal propeptide. When a mutant alpha GL-PLAP, in which the aspartic acid residue is replaced with tryptophan at a putative cleavage/attachment site, was expressed in COS-1 cells, the 25 kDa precursor was the only form found inside the cell and retained in the endoplasmic reticulum, as judged by immunofluorescence microscopy. In vitro translation programmed with mRNAs coding for the wild-type and mutant forms of alpha GL-PLAP demonstrated that the C-terminal propeptide was cleaved from the wild-type chimeric protein, but not from the mutant one. This gave rise to the 22 kDa form attached with a GPI anchor, suggesting that GPI is covalently linked to the aspartic acid residue (Asp159) of alpha GL-PLAP. Taken together, these results indicate that the C-terminal propeptide of PLAP functions as a signal to render alpha GL a GPI-linked membrane protein in vitro and in vivo in cultured cells, and that the chimeric protein constructed in this study may be useful for elucidating the mechanism underlying the cleavage of the propeptide and attachment of GPI, which occur in the endoplasmic reticulum.

Functional interaction between p21rap1A and components of the budding pathway in Saccharomyces cerevisiae

1992 ◽  
Vol 12 (9) ◽  
pp. 4084-4092
Author(s):  
P C McCabe ◽  
H Haubruck ◽  
P Polakis ◽  
F McCormick ◽  
M A Innis
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Mammalian Cells ◽  
Bound States ◽  
Yeast Cells ◽  
Temperature Sensitive ◽  
Wild Type ◽  
Amino Terminal ◽  
Loop Region

The rap1A gene encodes a 21-kDa, ras-related GTP-binding protein (p21rap1A) of unknown function. A close structural homolog of p21rap1A (65% identity in the amino-terminal two-thirds) is the RSR1 gene product (Rsr1p) of Saccharomyces cerevisiae. Although Rsr1p is not essential for growth, its presence is required for nonrandom selection of bud sites. To assess the similarity of these proteins at the functional level, wild-type and mutant forms of p21rap1A were tested for complementation of activities known to be fulfilled by Rsr1p. Expression of p21rap1A, like multicopy expression of RSR1, suppressed the conditional lethality of a temperature-sensitive cdc24 mutation. Point mutations predicted to affect the localization of p21rap1A or its ability to cycle between GDP and GTP-bound states disrupted suppression of cdc24ts, while other mutations in the 61-65 loop region improved suppression. Expression of p21rap1A could not, however, suppress the random budding phenotype of rsr1 cells. p21rap1A also apparently interfered with the normal activity of Rsrlp, causing random budding in diploid wild-type cells, suggesting an inability of p21rap1A to interact appropriately with Rsr1p regulatory proteins. Consistent with this hypothesis, we found an Rsr1p-specific GTPase-activating protein (GAP) activity in yeast membranes which was not active toward p21rap1A, indicating that p21rap1A may be predominantly GTP bound in yeast cells. Coexpression of human Rap1-specific GAP suppressed the random budding due to expression of p21rap1A or its derivatives, including Rap1AVal-12. Although Rap1-specific GAP stimulated the GTPase of Rsr1p in vitro, it did not dominantly interfere with Rsr1p function in vivo. A chimera consisting of Rap1A1-165::Rsr1p166-272 did not exhibit normal Rsr1p function in the budding pathway. These results indicated that p21rap1A and Rsr1p share at least partial functional homology, which may have implications for p21rap1A function in mammalian cells.

scholarly journals Limited ER quality control for GPI-anchored proteins

2016 ◽  
Vol 213 (6) ◽  
pp. 693-704 ◽  
Author(s):  
Natalia Sikorska ◽  
Leticia Lemus ◽  
Auxiliadora Aguilera-Romero ◽  
Javier Manzano-Lopez ◽  
Howard Riezman ◽  
...  
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Protein Folding ◽  
Misfolded Proteins ◽  
Control Mechanisms ◽  
Gpi Anchor ◽  
Er Quality Control ◽  
Entire Class ◽  
Er Export ◽  
Export Signal

Endoplasmic reticulum (ER) quality control mechanisms target terminally misfolded proteins for ER-associated degradation (ERAD). Misfolded glycophosphatidylinositol-anchored proteins (GPI-APs) are, however, generally poor ERAD substrates and are targeted mainly to the vacuole/lysosome for degradation, leading to predictions that a GPI anchor sterically obstructs ERAD. Here we analyzed the degradation of the misfolded GPI-AP Gas1* in yeast. We could efficiently route Gas1* to Hrd1-dependent ERAD and provide evidence that it contains a GPI anchor, ruling out that a GPI anchor obstructs ERAD. Instead, we show that the normally decreased susceptibility of Gas1* to ERAD is caused by canonical remodeling of its GPI anchor, which occurs in all GPI-APs and provides a protein-independent ER export signal. Thus, GPI anchor remodeling is independent of protein folding and leads to efficient ER export of even misfolded species. Our data imply that ER quality control is limited for the entire class of GPI-APs, many of them being clinically relevant.

Analysis of the function of the 70-kilodalton cyclase-associated protein (CAP) by using mutants of yeast adenylyl cyclase defective in CAP binding

1993 ◽  
Vol 13 (7) ◽  
pp. 4087-4097
Author(s):  
J Wang ◽  
N Suzuki ◽  
Y Nishida ◽  
T Kataoka
Keyword(s):  
Heat Shock ◽  
Adenylyl Cyclase ◽  
Gene Replacement ◽  
Yeast Cells ◽  
Cyclase Activity ◽  
In Vitro Mutagenesis ◽  
Wild Type ◽  
Adenylyl Cyclase Activity

In Saccharomyces cerevisiae, adenylyl cyclase forms a complex with the 70-kDa cyclase-associated protein (CAP). By in vitro mutagenesis, we assigned a CAP-binding site of adenylyl cyclase to a small segment near its C terminus and created mutants which lost the ability to bind CAP. CAP binding was assessed first by observing the ability of the overproduced C-terminal 150 residues of adenylyl cyclase to sequester CAP, thereby suppressing the heat shock sensitivity of yeast cells bearing the activated RAS2 gene (RAS2Val-19), and then by immunoprecipitability of adenylyl cyclase activity with anti-CAP antibody and by direct measurement of the amount of CAP bound. Yeast cells whose chromosomal adenylyl cyclase genes were replaced by the CAP-nonbinding mutants possessed adenylyl cyclase activity fully responsive to RAS2 protein in vitro. However, they did not exhibit sensitivity to heat shock in the RAS2Val-19 background. When glucose-induced accumulation of cyclic AMP (cAMP) was measured in these mutants carrying RAS2Val-19, a rapid transient rise indistinguishable from that of wild-type cells was observed and a high peak level and following persistent elevation of the cAMP concentration characteristic of RAS2Val-19 were abolished. In contrast, in the wild-type RAS2 background, similar cyclase gene replacement did not affect the glucose-induced cAMP response. These results suggest that the association with CAP, although not involved in the in vivo response to the wild-type RAS2 protein, is somehow required for the exaggerated response of adenylyl cyclase to activated RAS2.

scholarly journals Secretion ofSaccharomyces cerevisiaeKiller Toxin: Processing of the Glycosylated Precursor

1983 ◽  
Vol 3 (8) ◽  
pp. 1362-1370 ◽  
Author(s):  
H. Bussey ◽  
D. Saville ◽  
D. Greene ◽  
D. J. Tipper ◽  
K. A. Bostian
Keyword(s):  
Endoplasmic Reticulum ◽  
Secretory Pathway ◽  
Killer Toxin ◽  
Membrane System ◽  
Restrictive Temperature ◽  
Wild Type ◽  
Endoproteolytic Cleavage ◽  
Toxin Secretion

Killer toxin secretion was blocked at the restrictive temperature inSaccharomyces cerevisiae secmutants with conditional defects in theS. cerevisiaesecretory pathway leading to accumulation of endoplasmic reticulum (sec18), Golgi (sec7), or secretory vesicles (sec1). A 43,000-molecular-weight (43K) glycosylated protoxin was found by pulse-labeling in allsecmutants at the restrictive temperature. Insec18the protoxin was stable after a chase; but insec7andsec1the protoxin was unstable, and insec111K toxin was detected in cell lysates. The chymotrypsin inhibitor tosyl-l-phenylalanyl chloromethyl ketone (TPCK) blocked toxin secretion in vivo in wild-type cells by inhibiting protoxin cleavage. The unstable protoxin in wild-type and insec7andsec1cells at the restrictive temperature was stabilized by TPCK, suggesting that the protoxin cleavage was post-sec18and was mediated by a TPCK-inhibitable protease. Protoxin glycosylation was inhibited by tunicamycin, and a 36K protoxin was detected in inhibited cells. This 36K protoxin was processed, but toxin secretion was reduced 10-fold. We examined twokexmutants defective in toxin secretion; both synthesized a 43K protoxin, which was stable inkex1but unstable inkex2. Protoxin stability inkex1 kex2double mutants indicated the orderkex1→kex2in the protoxin processing pathway. TPCK did not block protoxin instability inkex2mutants. This suggested that theKEX1- andKEX2-dependent steps preceded thesec7Golgi block. We attempted to localize the protoxin inS. cerevisiaecells. Use of an in vitro rabbit reticulocyte-dog pancreas microsomal membrane system indicated that protoxin synthesized in vitro could be inserted into and glycosylated by the microsomal membranes. This membrane-associated protoxin was protected from trypsin proteolysis. Pulse-chased cells or spheroplasts, with or without TPCK, failed to secrete protoxin. The protoxin may not be secreted into the lumen of the endoplasmic reticulum, but may remain membrane associated and may require endoproteolytic cleavage for toxin secretion.

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