scholarly journals Mechanisms for Rescue of Correctable Folding Defects in CFTRΔF508

2009 ◽  
Vol 20 (18) ◽  
pp. 4059-4069 ◽  
Author(s):  
Diane E. Grove ◽  
Meredith F.N. Rosser ◽  
Hong Yu Ren ◽  
Anjaparavanda P. Naren ◽  
Douglas M. Cyr
Keyword(s):  
Cystic Fibrosis ◽  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Ubiquitin Ligase ◽  
Therapeutic Approach ◽  
Er Quality Control ◽  
Amino Terminal ◽  
Large Pool ◽  
Cellular Environment ◽  
R Domain

Premature degradation of CFTRΔF508 causes cystic fibrosis (CF). CFTRΔF508 folding defects are conditional and folding correctors are being developed as CF therapeutics. How the cellular environment impacts CFTRΔF508 folding efficiency and the identity of CFTRΔF508's correctable folding defects is unclear. We report that inactivation of the RMA1 or CHIP ubiquitin ligase permits a pool of CFTRΔF508 to escape the endoplasmic reticulum. Combined RMA1 or CHIP inactivation and Corr-4a treatment enhanced CFTRΔF508 folding to 3–7-fold greater levels than those elicited by Corr-4a. Some, but not all, folding defects in CFTRΔF508 are correctable. CHIP and RMA1 recognize different regions of CFTR and a large pool of nascent CFTRΔF508 is ubiquitinated by RMA1 before Corr-4a action. RMA1 recognizes defects in CFTRΔF508 related to misassembly of a complex that contains MSD1, NBD1, and the R-domain. Corr-4a acts on CFTRΔF508 after MSD2 synthesis and was ineffective at rescue of ΔF508 dependent folding defects in amino-terminal regions. In contrast, misfolding caused by the rare CF-causing mutation V232D in MSD1 was highly correctable by Corr-4a. Overall, correction of folding defects recognized by RMA1 and/or global modulation of ER quality control has the potential to increase CFTRΔF508 folding and provide a therapeutic approach for CF.

scholarly journals USP13 antagonizes gp78 to maintain functionality of a chaperone in ER-associated degradation

eLife ◽  
2014 ◽  
Vol 3 ◽  
Author(s):  
Yanfen Liu ◽  
Nia Soetandyo ◽  
Jin-gu Lee ◽  
Liping Liu ◽  
Yue Xu ◽  
...  
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Substrate Specificity ◽  
Ubiquitin Ligase ◽  
Proteolytic Processing ◽  
Misfolded Proteins ◽  
Physiological Adaptation ◽  
Er Quality Control ◽  
Proteotoxic Stress ◽  
Chaperone Complex

Physiological adaptation to proteotoxic stress in the endoplasmic reticulum (ER) requires retrotranslocation of misfolded proteins into the cytoplasm for ubiquitination and elimination by ER-associated degradation (ERAD). A surprising paradox emerging from recent studies is that ubiquitin ligases (E3s) and deubiquitinases (DUBs), enzymes with opposing activities, can both promote ERAD. Here we demonstrate that the ERAD E3 gp78 can ubiquitinate not only ERAD substrates, but also the machinery protein Ubl4A, a key component of the Bag6 chaperone complex. Remarkably, instead of targeting Ubl4A for degradation, polyubiquitination is associated with irreversible proteolytic processing and inactivation of Bag6. Importantly, we identify USP13 as a gp78-associated DUB that eliminates ubiquitin conjugates from Ubl4A to maintain the functionality of Bag6. Our study reveals an unexpected paradigm in which a DUB prevents undesired ubiquitination to sharpen substrate specificity for an associated ubiquitin ligase partner and to promote ER quality control.

scholarly journals Single, context-specific glycans can target misfolded glycoproteins for ER-associated degradation

2005 ◽  
Vol 169 (1) ◽  
pp. 73-82 ◽  
Author(s):  
Eric D. Spear ◽  
Davis T.W. Ng
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Secretory Protein ◽  
Carboxypeptidase Y ◽  
Er Quality Control ◽  
Systematic Analysis ◽  
Proteinase A ◽  
Context Specific ◽  
The Relationship ◽  
Erad Pathway

The endoplasmic reticulum (ER) maintains an environment essential for secretory protein folding. Consequently, the premature transport of polypeptides would be harmful to the cell. To avert this scenario, mechanisms collectively termed “ER quality control” prevent the transport of nascent polypeptides until they properly fold. Irreversibly misfolded molecules are sorted for disposal by the ER-associated degradation (ERAD) pathway. To better understand the relationship between quality control and ERAD, we studied a new misfolded variant of carboxypeptidase Y (CPY). The molecule was recognized and retained by ER quality control but failed to enter the ERAD pathway. Systematic analysis revealed that a single, specific N-linked glycan of CPY was required for sorting into the pathway. The determinant is dependent on the putative lectin-like receptor Htm1/Mnl1p. The discovery of a similar signal in misfolded proteinase A supported the generality of the mechanism. These studies show that specific signals embedded in glycoproteins can direct their degradation if they fail to fold.

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.

scholarly journals Overlapping function of Hrd1 and Ste24 in translocon quality control provides robust channel surveillance

2020 ◽  
Vol 295 (47) ◽  
pp. 16113-16120
Author(s):  
Avery M. Runnebohm ◽  
Kyle A. Richards ◽  
Courtney Broshar Irelan ◽  
Samantha M. Turk ◽  
Halie E. Vitali ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Ubiquitin Ligase ◽  
Biological Membranes ◽  
The Other ◽  
Growth Defect ◽  
Zinc Metalloprotease

Translocation of proteins across biological membranes is essential for life. Proteins that clog the endoplasmic reticulum (ER) translocon prevent the movement of other proteins into the ER. Eukaryotes have multiple translocon quality control (TQC) mechanisms to detect and destroy proteins that persistently engage the translocon. TQC mechanisms have been defined using a limited panel of substrates that aberrantly occupy the channel. The extent of substrate overlap among TQC pathways is unknown. In this study, we found that two TQC enzymes, the ER-associated degradation ubiquitin ligase Hrd1 and zinc metalloprotease Ste24, promote degradation of characterized translocon-associated substrates of the other enzyme in Saccharomyces cerevisiae. Although both enzymes contribute to substrate turnover, our results suggest a prominent role for Hrd1 in TQC. Yeast lacking both Hrd1 and Ste24 exhibit a profound growth defect, consistent with overlapping function. Remarkably, two mutations that mildly perturb post-translational translocation and reduce the extent of aberrant translocon engagement by a model substrate diminish cellular dependence on TQC enzymes. Our data reveal previously unappreciated mechanistic complexity in TQC substrate detection and suggest that a robust translocon surveillance infrastructure maintains functional and efficient translocation machinery.

scholarly journals Endoplasmic reticulum chaperones participate in human cytomegalovirus US2-mediated degradation of class I major histocompatibility complex molecules

2008 ◽  
Vol 89 (5) ◽  
pp. 1122-1130 ◽  
Author(s):  
Kristina Oresic ◽  
Domenico Tortorella
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Major Histocompatibility Complex ◽  
Human Cytomegalovirus ◽  
Class I ◽  
Cell Surface Expression ◽  
Major Histocompatibility ◽  
Er Quality Control ◽  
Heavy Chains ◽  
Histocompatibility Complex

Inhibition of cell-surface expression of major histocompatibility complex class I molecules by human cytomegalovirus (HCMV, a β-herpesvirus) promotes escape from recognition by CD8+ cytotoxic T cells. The HCMV US2 and US11 gene products induce class I downregulation during the early phase of HCMV infection by facilitating the degradation of class I heavy chains. The HCMV proteins promote the transport of the class I heavy chains across the endoplasmic reticulum (ER) membrane into the cytosol by a process referred to as ‘dislocation’, which is then followed by proteasome degradation. This process has striking similarities to the degradation of misfolded ER proteins mediated by ER quality control. Even though the major steps of the dislocation reaction have been characterized, the cellular proteins, specifically the ER chaperones involved in targeting class I for dislocation, have not been fully delineated. To elucidate the chaperones involved in HCMV-mediated class I dislocation, we utilized a chimeric class I heavy chain with an affinity tag at its carboxy terminus. Interestingly, US2 but not US11 continued to target the class I chimera for destruction, suggesting a structural limitation for US11-mediated degradation. Association studies in US2 cells and in cells that express a US2 mutant, US2–186HA, revealed that class I specifically interacts with calnexin, BiP and calreticulin. These findings demonstrate that US2-mediated class I destruction utilizes specific chaperones to facilitate class I dislocation. The data suggest a more general model in which the chaperones that mediate protein folding may also function during ER quality control to eliminate aberrant ER proteins.

scholarly journals In Vivo Action of the HRD Ubiquitin Ligase Complex: Mechanisms of Endoplasmic Reticulum Quality Control and Sterol Regulation

2001 ◽  
Vol 21 (13) ◽  
pp. 4276-4291 ◽  
Author(s):  
Richard G. Gardner ◽  
Alexander G. Shearer ◽  
Randolph Y. Hampton
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Ubiquitin Ligase ◽  
Sequence Similarity ◽  
High Specificity ◽  
Specific Sequence ◽  
Ubiquitin Ligase Complex ◽  
Ubiquitin Conjugating Enzyme ◽  
Conjugating Enzyme

ABSTRACT Ubiquitination is used to target both normal proteins for specific regulated degradation and misfolded proteins for purposes of quality control destruction. Ubiquitin ligases, or E3 proteins, promote ubiquitination by effecting the specific transfer of ubiquitin from the correct ubiquitin-conjugating enzyme, or E2 protein, to the target substrate. Substrate specificity is usually determined by specific sequence determinants, or degrons, in the target substrate that are recognized by the ubiquitin ligase. In quality control, however, a potentially vast collection of proteins with characteristic hallmarks of misfolding or misassembly are targeted with high specificity despite the lack of any sequence similarity between substrates. In order to understand the mechanisms of quality control ubiquitination, we have focused our attention on the first characterized quality control ubiquitin ligase, the HRD complex, which is responsible for the endoplasmic reticulum (ER)-associated degradation (ERAD) of numerous ER-resident proteins. Using an in vivo cross-linking assay, we directly examined the association of the separate HRDcomplex components with various ERAD substrates. We have discovered that the HRD ubiquitin ligase complex associates with both ERAD substrates and stable proteins, but only mediates ubiquitin-conjugating enzyme association with ERAD substrates. Our studies with the sterol pathway-regulated ERAD substrate Hmg2p, an isozyme of the yeast cholesterol biosynthetic enzyme HMG-coenzyme A reductase (HMGR), indicated that the HRD complex discerns between a degradation-competent “misfolded” state and a stable, tightly folded state. Thus, it appears that the physiologically regulated, HRD-dependent degradation of HMGR is effected by a programmed structural transition from a stable protein to a quality control substrate.

scholarly journals The Cochaperone HspBP1 Inhibits the CHIP Ubiquitin Ligase and Stimulates the Maturation of the Cystic Fibrosis Transmembrane Conductance Regulator

2004 ◽  
Vol 15 (9) ◽  
pp. 4003-4010 ◽  
Author(s):  
Simon Alberti ◽  
Karsten Böhse ◽  
Verena Arndt ◽  
Anton Schmitz ◽  
Jörg Höhfeld
Keyword(s):  
Cystic Fibrosis ◽  
Quality Control ◽  
Ubiquitin Ligase ◽  
Molecular Chaperones ◽  
Protein Quality ◽  
Regulatory Mechanism ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Ubiquitin Ligase Activity ◽  
Cystic Fibrosis Transmembrane

The CHIP ubiquitin ligase turns molecular chaperones into protein degradation factors. CHIP associates with the chaperones Hsc70 and Hsp90 during the regulation of signaling pathways and during protein quality control, and directs chaperone-bound clients to the proteasome for degradation. Obviously, this destructive activity should be carefully controlled. Here, we identify the cochaperone HspBP1 as an inhibitor of CHIP. HspBP1 attenuates the ubiquitin ligase activity of CHIP when complexed with Hsc70. As a consequence, HspBP1 interferes with the CHIP-induced degradation of immature forms of the cystic fibrosis transmembrane conductance regulator (CFTR) and stimulates CFTR maturation. Our data reveal a novel regulatory mechanism that determines folding and degradation activities of molecular chaperones.

scholarly journals Yos9p assists in the degradation of certain nonglycosylated proteins from the endoplasmic reticulum

2011 ◽  
Vol 22 (16) ◽  
pp. 2937-2945 ◽  
Author(s):  
Laura A. Jaenicke ◽  
Holger Brendebach ◽  
Matthias Selbach ◽  
Christian Hirsch
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Ubiquitin Ligase ◽  
Quantitative Proteomics ◽  
Structural Defects ◽  
Sterol Synthesis ◽  
Mutant Variant ◽  
Substrate Spectrum

The HRD ubiquitin ligase recognizes and ubiquitylates proteins of the endoplasmic reticulum that display structural defects. Here, we apply quantitative proteomics to characterize the substrate spectrum of the HRD complex. Among the identified substrates is Erg3p, a glycoprotein involved in sterol synthesis. We characterize Erg3p and demonstrate that the elimination of Erg3p requires Htm1p and Yos9p, two proteins that take part in the glycan-dependent turnover of aberrant proteins. We further show that the HRD ligase also mediates the breakdown of Erg3p and CPY* engineered to lack N-glycans. The degradation of these nonglycosylated substrates is enhanced by a mutant variant of Yos9p that has lost its affinity for oligosaccharides, indicating that Yos9p has a previously unrecognized role in the quality control of nonglycosylated proteins.

scholarly journals Exposure of bipartite hydrophobic signal triggers nuclear quality control of Ndc10 at the endoplasmic reticulum/nuclear envelope

2011 ◽  
Vol 22 (24) ◽  
pp. 4726-4739 ◽  
Author(s):  
Noa Furth ◽  
Or Gertman ◽  
Ayala Shiber ◽  
Omri S. Alfassy ◽  
Itamar Cohen ◽  
...  
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Protein Folding ◽  
Nuclear Envelope ◽  
Reverse Genetics ◽  
Point Mutations ◽  
Hydrophobic Surface ◽  
Structural Features ◽  
Er Quality Control ◽  
C Terminus

Proper functioning of the protein-folding quality control network depends on the network's ability to discern diverse structural perturbations to the native states of its protein substrates. Despite the centrality of the detection of misfolded states to cell home­ostasis, very little is known about the exact sequence and structural features that mark a protein as being misfolded. To investigate these features, we studied the requirements for the degradation of the yeast kinetochore protein Ndc10p. Mutant Ndc10p is a substrate of a protein-folding quality control pathway mediated by the E3 ubiquitin (Ub) ligase Doa10p at the endoplasmic reticulum (ER)/nuclear envelope membrane. Analysis of Ndc10p mutant derivatives, employing a reverse genetics approach, identified an autonomous quality control–associated degradation motif near the C-terminus of the protein. This motif is composed of two indispensable hydrophobic elements: a hydrophobic surface of an amphipathic helix and a loosely structured hydrophobic C-terminal tail. Site-specific point mutations expose these elements, triggering ubiquitin-mediated and HSP70 chaperone–dependent degradation of Ndc10p. These findings substantiate the ability of the ER quality control system to recognize subtle perturbation(s) in the native structure of a nuclear protein.

scholarly journals Aberrant substrate engagement of the ER translocon triggers degradation by the Hrd1 ubiquitin ligase

2012 ◽  
Vol 197 (6) ◽  
pp. 761-773 ◽  
Author(s):  
Eric M. Rubenstein ◽  
Stefan G. Kreft ◽  
Wesley Greenblatt ◽  
Robert Swanson ◽  
Mark Hochstrasser
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Ubiquitin Ligase ◽  
Apolipoprotein B ◽  
Secretory Pathway ◽  
Protein A ◽  
Proteasomal Degradation ◽  
Membrane Localization ◽  
General Role

Little is known about quality control of proteins that aberrantly or persistently engage the endoplasmic reticulum (ER)-localized translocon en route to membrane localization or the secretory pathway. Hrd1 and Doa10, the primary ubiquitin ligases that function in ER-associated degradation (ERAD) in yeast, target distinct subsets of misfolded or otherwise abnormal proteins based primarily on degradation signal (degron) location. We report the surprising observation that fusing Deg1, a cytoplasmic degron normally recognized by Doa10, to the Sec62 membrane protein rendered the protein a Hrd1 substrate. Hrd1-dependent degradation occurred when Deg1-Sec62 aberrantly engaged the Sec61 translocon channel and underwent topological rearrangement. Mutations that prevent translocon engagement caused a reversion to Doa10-dependent degradation. Similarly, a variant of apolipoprotein B, a protein known to be cotranslocationally targeted for proteasomal degradation, was also a Hrd1 substrate. Hrd1 therefore likely plays a general role in targeting proteins that persistently associate with and potentially obstruct the translocon.

Sign in / Sign up

Export Citation Format

Share Document