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 Modularity of the Hrd1 ERAD complex underlies its diverse client range

2010 ◽  
Vol 188 (5) ◽  
pp. 707-716 ◽  
Author(s):  
Kazue Kanehara ◽  
Wei Xie ◽  
Davis T.W. Ng
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Protein Folding ◽  
Membrane Proteins ◽  
Secretory Protein ◽  
Modular Organization ◽  
Control Mechanisms ◽  
Core Complex ◽  
Er Quality Control ◽  
Folding State

Secretory protein folding is monitored by endoplasmic reticulum (ER) quality control mechanisms. Misfolded proteins are retained and targeted to ER-associated degradation (ERAD) pathways. At their core are E3 ubiquitin ligases, which organize factors that recognize, ubiquitinate, and translocate substrates. Of these, we report that the Hrd1 complex manages three distinct substrate classes. A core complex is required for all classes and is sufficient for some membrane proteins. The accessory factors Usa1p and Der1p adapt the complex to process luminal substrates. Their integration is sufficient to process molecules bearing glycan-independent degradation signals. The presence of Yos9p extends the substrate range by mediating the recognition of glycan-based degradation signals. This modular organization enables the Hrd1 complex to recognize topologically diverse substrates. The Hrd1 system does not directly evaluate the folding state of polypeptides. Instead, it does so indirectly, by recognizing specific embedded signals displayed upon misfolding.

scholarly journals Evasion of Endoplasmic Reticulum Surveillance Makes Wsc1p an Obligate Substrate of Golgi Quality Control

2010 ◽  
Vol 21 (7) ◽  
pp. 1153-1165 ◽  
Author(s):  
Songyu Wang ◽  
Davis T.W. Ng
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Secretory Pathway ◽  
Control Mechanisms ◽  
Mutant Proteins ◽  
Engineered Substrates ◽  
Pathway Analyses ◽  
Er Export ◽  
First Time ◽  
Export Signal

In the endoplasmic reticulum (ER), most newly synthesized proteins are retained by quality control mechanisms until folded. Misfolded molecules are sorted to ER-associated degradation (ERAD) pathways for disposal. Reports of mutant proteins degraded in the vacuole/lysosome suggested an independent Golgi-based mechanism also at work. Although little is understood of the post-ER pathway, the growing number of variants using it suggests a major role in quality control. Why seemingly redundant mechanisms in sequential compartments are needed is unclear. To understand their physiological relationship, the identification of endogenous pathway-specific substrates is a prerequisite. With ERAD substrates already well characterized, the discovery of Wsc1p as an obligate substrate of Golgi quality control enabled detailed cross-pathway analyses for the first time. By analyzing a panel of engineered substrates, the data show that the surveillance mode is determined by each polypeptide's intrinsic design. Although most secretory pathway proteins can display ERAD determinants when misfolded, the lack thereof shields Wsc1p from inspection by ER surveillance. Additionally, a powerful ER export signal mediates transport whether the luminal domain is folded or not. By evading ERAD through these passive and active mechanisms, Wsc1p is fully dependent on the post-ER system for its quality control.

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 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 A cross-kingdom conserved ER-phagy receptor maintains endoplasmic reticulum homeostasis during stress

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Madlen Stephani ◽  
Lorenzo Picchianti ◽  
Alexander Gajic ◽  
Rebecca Beveridge ◽  
Emilio Skarwan ◽  
...  
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Mammalian Cells ◽  
Control Mechanisms ◽  
Receptor Complex ◽  
Er Quality Control ◽  
Proteotoxic Stress ◽  
Quality Control Mechanism ◽  
Passenger Proteins

Eukaryotes have evolved various quality control mechanisms to promote proteostasis in the endoplasmic reticulum (ER). Selective removal of certain ER domains via autophagy (termed as ER-phagy) has emerged as a major quality control mechanism. However, the degree to which ER-phagy is employed by other branches of ER-quality control remains largely elusive. Here, we identify a cytosolic protein, C53, that is specifically recruited to autophagosomes during ER-stress, in both plant and mammalian cells. C53 interacts with ATG8 via a distinct binding epitope, featuring a shuffled ATG8 interacting motif (sAIM). C53 senses proteotoxic stress in the ER lumen by forming a tripartite receptor complex with the ER-associated ufmylation ligase UFL1 and its membrane adaptor DDRGK1. The C53/UFL1/DDRGK1 receptor complex is activated by stalled ribosomes and induces the degradation of internal or passenger proteins in the ER. Consistently, the C53 receptor complex and ufmylation mutants are highly susceptible to ER stress. Thus, C53 forms an ancient quality control pathway that bridges selective autophagy with ribosome-associated quality control in the ER.

scholarly journals Bap31 Is an Itinerant Protein That Moves between the Peripheral Endoplasmic Reticulum (ER) and a Juxtanuclear Compartment Related to ER-associated Degradation

2008 ◽  
Vol 19 (5) ◽  
pp. 1825-1836 ◽  
Author(s):  
Yuichi Wakana ◽  
Sawako Takai ◽  
Ken-ichi Nakajima ◽  
Katsuko Tani ◽  
Akitsugu Yamamoto ◽  
...  
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Transmembrane Proteins ◽  
Transmembrane Domains ◽  
Er Quality Control ◽  
Transport Pathways ◽  
The Third ◽  
Intermediate Compartment ◽  
Er Export ◽  
Control Compartment

Certain endoplasmic reticulum (ER)-associated degradation (ERAD) substrates with transmembrane domains are segregated from other ER proteins and sorted into a juxtanuclear subcompartment, known as the ER quality control compartment. Bap31 is an ER protein with three transmembrane domains, and it is assumed to be a cargo receptor for ER export of some transmembrane proteins, especially those prone to ERAD. Here, we show that Bap31 is a component of the ER quality control compartment and that it moves between the peripheral ER and a juxtanuclear ER or ER-related compartment distinct from the conventional ER–Golgi intermediate compartment. The third and second transmembrane domains of Bap31 are principally responsible for the movement to and recycling from the juxtanuclear region, respectively. This cycling was blocked by depolymerization of microtubules and disruption of dynein–dynactin function. Overexpression of Sar1p and Arf1 mutants affected Bap31 cycling, suggesting that this cycling pathway is related to the conventional vesicular transport pathways.

scholarly journals Tay–Sachs disease mutations in HEXA target the α chain of hexosaminidase A to endoplasmic reticulum–associated degradation

2016 ◽  
Vol 27 (24) ◽  
pp. 3813-3827 ◽  
Author(s):  
Devin Dersh ◽  
Yuichiro Iwamoto ◽  
Yair Argon
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Control Mechanisms ◽  
Permissive Temperature ◽  
Lysosomal Storage ◽  
Loss Of Function ◽  
Er Quality Control ◽  
Tay Sachs Disease ◽  
Hexosaminidase A ◽  
Α Chain

Loss of function of the enzyme β-hexosaminidase A (HexA) causes the lysosomal storage disorder Tay–Sachs disease (TSD). It has been proposed that mutations in the α chain of HexA can impair folding, enzyme assembly, and/or trafficking, yet there is surprisingly little known about the mechanisms of these potential routes of pathogenesis. We therefore investigated the biosynthesis and trafficking of TSD-associated HexA α mutants, seeking to identify relevant cellular quality control mechanisms. The α mutants E482K and G269S are defective in enzymatic activity, unprocessed by lysosomal proteases, and exhibit altered folding pathways compared with wild-type α. E482K is more severely misfolded than G269S, as observed by its aggregation and inability to associate with the HexA β chain. Importantly, both mutants are retrotranslocated from the endoplasmic reticulum (ER) to the cytosol and are degraded by the proteasome, indicating that they are cleared via ER-associated degradation (ERAD). Leveraging these discoveries, we observed that manipulating the cellular folding environment or ERAD pathways can alter the kinetics of mutant α degradation. Additionally, growth of patient fibroblasts at a permissive temperature or with chemical chaperones increases cellular Hex activity by improving mutant α folding. Therefore modulation of the ER quality control systems may be a potential therapeutic route for improving some forms of TSD.

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 Inhibiting Endoplasmic Reticulum (ER)-associated Degradation of Misfolded Yor1p Does Not Permit ER Export Despite the Presence of a Diacidic Sorting Signal

2007 ◽  
Vol 18 (9) ◽  
pp. 3398-3413 ◽  
Author(s):  
Silvere Pagant ◽  
Leslie Kung ◽  
Mariana Dorrington ◽  
Marcus C.S. Lee ◽  
Elizabeth A. Miller
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Secretory Pathway ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Er Quality Control ◽  
Er Retention ◽  
Copii Vesicles ◽  
Er Export ◽  
Cystic Fibrosis Transmembrane

Capture of newly synthesized proteins into endoplasmic reticulum (ER)-derived coat protomer type II (COPII) vesicles represents a critical juncture in the quality control of protein biogenesis within the secretory pathway. The yeast ATP-binding cassette transporter Yor1p is a pleiotropic drug pump that shows homology to the human cystic fibrosis transmembrane conductance regulator (CFTR). Deletion of a phenylalanine residue in Yor1p, equivalent to the major disease-causing mutation in CFTR, causes ER retention and degradation via ER-associated degradation. We have examined the relationship between protein folding, ERAD and forward transport during Yor1p biogenesis. Uptake of Yor1p into COPII vesicles is mediated by an N-terminal diacidic signal that likely interacts with the “B-site” cargo-recognition domain on the COPII subunit, Sec24p. Yor1p-ΔF is subjected to complex ER quality control involving multiple cytoplasmic chaperones and degradative pathways. Stabilization of Yor1p-ΔF by inhibiting its degradation does not permit access of Yor1p-ΔF to COPII vesicles. We propose that the ER quality control checkpoint engages misfolded Yor1p even after it has been stabilized by inhibition of the degradative pathway.

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.

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