Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.25.1 (proteasome)
28,817 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Peptide N-glycanase (PNGase) is involved in the cleavage of oligosaccharide chains from misfolded glycoproteins that are destined for degradation by the proteasome. Earlier, a number of potential binding partners of mouse PNGase (mPNGase) were detected by using the yeast two-hybrid system. In the current study, an in vitro system was set up to investigate direct interactions between mPNGase and these candidate proteins. Although the yeast two-hybrid system suggested an interaction of six different proteins with mPNGase, only mHR23B and the proteasome subunit mS4 were found to interact with mPNGase. In fact, mS4 competes with mHR23B for binding to mPNGase. These results suggested two possible pathways for the interaction between mPNGase and the proteasome. In one pathway, mHR23B mediates the interaction between mPNGase and the proteasome. In an alternative pathway, mPNGase directly binds to the proteasome subunit, mS4. In either case, it is clear that PNGase is located in close proximity to the proteasome and is available for deglycosylation of glycoproteins destined for degradation. Surprisingly, mPNGase also was found to mediate binding of the cytoplasmic protein, p97, to the proteasome through the formation of a ternary complex made up of mHR23B, mPNGase, and p97. Because p97 is known to bind to the endoplasmic reticulum membrane protein AMFR (gp78), an E3 ligase, we propose a model in which p97, mPNGase, and mHR23B mediate interaction of the endoplasmic reticulum with the proteasome.
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PMID:Multiple modes of interaction of the deglycosylation enzyme, mouse peptide N-glycanase, with the proteasome. 1624 33

Mouse peptide N-glycanase (mPNGase) cleaves the N-glycan chain from misfolded glycoproteins and glycopeptides. Previously, several proteins were found to directly interact with mPNGase; among them, both mHR23B and mS4 were found to link mPNGase to the proteasome. In this study, we found that the cytoplasmic protein mp97 participates in the formation of a ternary complex containing mouse autocrine motility factor receptor (mAMFR), mp97, and mPNGase. This assemblage recruits the cytosolic mPNGase close to the endoplasmic reticulum (ER) membrane, where the retrotranslocation of misfolded glycoproteins is thought to occur. In addition to the ER membrane-associated E3 ligase mAMFR, a cytosolic protein mY33K, containing both UBA and UBX domains, was found to also directly interact with mp97. Thus, a complex containing five proteins, mAMFR, mY33K, mp97, mPNGase, and mHR23B, is formed in close proximity to the ER membrane and serves to couple the activities of retrotranslocation, ubiquitination, and deglycosylation and, thereby, route misfolded glycoproteins to the proteasome.
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PMID:The AAA ATPase p97 links peptide N-glycanase to the endoplasmic reticulum-associated E3 ligase autocrine motility factor receptor. 1670 68

The AAA ATPase p97 is a ubiquitin-selective molecular machine involved in multiple cellular processes, including protein degradation through the ubiquitin-proteasome system and homotypic membrane fusion. Specific p97 functions are mediated by a variety of cofactors, among them peptide N-glycanase, an enzyme that removes glycans from misfolded glycoproteins. Here we report the three-dimensional structure of the aminoterminal PUB domain of human peptide N-glycanase. We demonstrate that the PUB domain is a novel p97 binding module interacting with the D1 and/or D2 ATPase domains of p97 and identify an evolutionary conserved surface patch required for p97 binding. Furthermore, we show that the PUB and UBX domains do not bind to p97 in a mutually exclusive manner. Our results suggest that PUB domain-containing proteins constitute a widespread family of diverse p97 cofactors.
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PMID:The PUB domain functions as a p97 binding module in human peptide N-glycanase. 1680 42

The endoplasmic-reticulum-associated degradation of misfolded (glyco)proteins ensures that only functional, correctly folded proteins exit from the endoplasmic reticulum and that misfolded ones are degraded by the ubiquitin-proteasome system. During the degradation of misfolded glycoproteins, they are deglycosylated by the PNGase (peptide:N-glycanase). The free oligosaccharides released by PNGase are known to be further catabolized by a cytosolic alpha-mannosidase, although the gene encoding this enzyme has not been identified unequivocally. The findings in the present study demonstrate that an alpha-mannosidase, Man2C1, is involved in the processing of free oligosaccharides that are formed in the cytosol. When the human Man2C1 orthologue was expressed in HEK-293 cells, most of the enzyme was localized in the cytosol. Its activity was enhanced by Co2+, typical of other known cytosolic alpha-mannosidases so far characterized from animal cells. The down-regulation of Man2C1 activity by a small interfering RNA drastically changed the amount and structure of oligosaccharides accumulating in the cytosol, demonstrating that Man2C1 indeed is involved in free oligosaccharide processing in the cytosol. The oligosaccharide processing in the cytosol by PNGase, endo-beta-N-acetylglucosaminidase and alpha-mannosidase may represent the common 'non-lysosomal' catabolic pathway for N-glycans in animal cells, although the molecular mechanism as well as the functional importance of such processes remains to be determined.
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PMID:Man2C1, an alpha-mannosidase, is involved in the trimming of free oligosaccharides in the cytosol. 1684 60

The inability of certain N-linked glycoproteins to adopt their native conformation in the endoplasmic reticulum (ER) leads to their retrotranslocation into the cytosol and subsequent degradation by the proteasome. In this pathway the cytosolic peptide-N-glycanase (PNGase) cleaves the N-linked glycan chains off denatured glycoproteins. PNGase is highly conserved in eukaryotes and plays an important role in ER-associated protein degradation. In higher eukaryotes, PNGase has an N-terminal and a C-terminal extension in addition to its central catalytic domain, which is structurally and functionally related to transglutaminases. Although the N-terminal domain of PNGase is involved in protein-protein interactions, the function of the C-terminal domain has not previously been characterized. Here, we describe biophysical, biochemical, and crystallographic studies of the mouse PNGase C-terminal domain, including visualization of a complex between this domain and mannopentaose. These studies demonstrate that the C-terminal domain binds to the mannose moieties of N-linked oligosaccharide chains, and we further show that it enhances the activity of the mouse PNGase core domain, presumably by increasing the affinity of mouse PNGase for the glycan chains of misfolded glycoproteins.
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PMID:Structural and biochemical studies of the C-terminal domain of mouse peptide-N-glycanase identify it as a mannose-binding module. 1708 51

A cytoplasmic peptide:N-glycanase (PNGase) has been implicated in the proteasomal degradation of aberrant glycoproteins synthesized in the endoplasmic reticulum. The reaction is believed to be important for subsequent proteolysis by the proteasome since bulky N-glycan chains on misfolded glycoproteins may impair their efficient entry into the interior of the cylinder-shaped 20S proteasome, where the active sites of the proteases reside. The deglycosylation reaction by PNGase brings about two major changes on substrate proteins; one is a removal of N-glycan chains, and the other is the introduction of negative charge(s) into the core peptide by converting glycosylated asparagine residue(s) into aspartic acid residue(s). Therefore, PNGase action can be accurately monitored by detecting both changes using two different methods; that is, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for deglycosylation and isoelectric focusing for detection of introduction of negative charge(s) into core proteins. This chapter will describe the simple in vivo as well as in vitro assay method to detect PNGase activity.
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PMID:A cytoplasmic peptide: N-glycanase. 1711 67

Peptide:N-glycanase has been thought to be responsible for proteasome-dependent degradation of misfolded glycoproteins translocated from the endoplasmic reticulum (ER) to the cytosol. Therefore, the enzyme was supposed to be able to distinguish between native and non-native glycoproteins. In the present study, a recombinant, yeast peptide:N-glycanase, Png1p, was expressed in Escherichia coli as inclusion bodies and was purified, refolded and characterized. The results showed that the recombinant enzyme has a broad pH range adaptation, from pH 4.0 to pH 10.0, and has an optimum temperature of 30 degrees C. This enzyme is a zinc metalloenzyme. Its activity was abolished with the addition of EDTA and not restored by adding metal ions. Furthermore, the deglycosylation efficiency of recombinant Png1p from E. coli was investigated with respect to the substrate conformation in vitro. When ribonuclease B (RNase B) was denatured at 60-65 degrees C or by 40-60 mM dithiothreitol, indicated by its obvious structural change and sharpest activity change, its deglycosylation by Png1p was most prominent. The deglycosylation efficiency of RNase B by Png1p was found to be related to its structural conformation and enzymatic activity.
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PMID:Influence of substrate conformation on the deglycosylation of ribonuclease B by recombinant yeast peptide:N-glycanase. 1721 53

The endoplasmic reticulum-associated degradation (ERAD) of misfolded (glyco)proteins ensures that only functional, correctly folded proteins exit from the ER and that misfolded ones are degraded by the ubiquitin-proteasome system. During the degradation of misfolded glycoproteins, some of them are subjected to deglycosylation by the cytoplasmic peptide:N-glycanase (PNGase). The cytosolic PNGase is widely distributed throughout eukaryotes. Here we show that the nematode Caenorhabditis elegans PNG-1, the cytoplasmic PNGase orthologue in this organism, exhibits dual enzyme functions, not only as PNGase but also as an oxidoreductase (thioredoxin). Using an in vitro assay as well as an in vivo assay system in budding yeast, the N-terminal thioredoxin domain and the central transglutaminase domain were found to be essential for oxidoreductase activity and PNGase activity, respectively. Occurrence of a C. elegans mutation affecting a catalytic residue in the PNGase domain strongly suggests the functional importance of this protein in higher eukaryotes.
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PMID:Dual enzymatic properties of the cytoplasmic peptide: N-glycanase in C. elegans. 1750 31

Quality control of proteins is an essential process for maintaining normal cell activity. It ensures that only correctly folded proteins are produced and terminally misfolded proteins are eliminated by degradation. ER-associated degradation (ERAD) of misfolded proteins is an important aspect of protein quality control system. Recent studies have revealed that glycoprotein glycans play significant roles in this process. It includes polyubiquitination, deglycosylation, and proteasomal degradation. In the present study, a systematic analysis of these steps was carried out using chemically synthesized glycopeptides. We revealed that N-linked glycopeptides are degraded by 20S proteasome, but with drastically reduced rate compared to non-glycosylated peptide. This result strongly suggests that deglycosylating activity of peptide:N-glycanase (PNGase) is important for the facile degradation of glycoproteins. Our study showed, for the first time, that PNGase cleaves truncated glycans as short as chitobiose from peptide. However, this cleavage required the presence of hydrophobic region nearby N-glycosylation site. Furthermore, analysis of interactions with F-box protein Fbs1 was conducted with fluorescent correlation spectroscopy (FCS). It was shown that the presence of Fbs1 perturb the activity of PNGase toward high-mannose-type glycopeptides.
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PMID:Analysis of ER-associated glycoprotein degradation using synthetic glycopeptide probes. 1759 22

The addition of N-linked glycans to nascent polypeptides occurs cotranslationally in the endoplasmic reticulum (ER). For many proteins the state of the glycans serves as an indicator, which allows the ER quality control system to monitor the conformation of polypeptides upon folding. Proteins that fail to fold in the ER are often dislocated to the cytoplasm, where they are subjected to proteasomal degradation. Although the addition of N-linked glycans occurs within the ER, non-lysosomal removal of the glycans occurs in the cytosol by the action of peptide N-glycanase (PNGase). In this study, we investigated the interplay between PNGase action and proteasomal degradation of ER misfolded proteins (i.e. whether PNGase acts prior to or following proteasomal degradation). Interestingly, we found that glycan removal from N-terminally extended peptides modulates the presentation of class I major histocompatibility complex-restricted epitopes. Our findings provide direct evidence that the proteasome is capable of degrading glycoproteins without prior removal of their glycans. This degradation is independent of either the identity of the glycosylated protein or the type and number of N-linked glycans it harbors. We also captured and characterized glycopeptides generated following proteasomal degradation of RNaseB. Although the carbohydrate moiety reduced the variability of the degradation products that include the glycosylated residue (local effect), the overall global digestion pattern of RNaseB was unaffected. Together with earlier findings by others, our data support a model in which PNGase may act both upstream and downstream to proteasomal degradation and demonstrates its important role in class I major histocompatibility complex antigen presentation.
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PMID:N-linked glycosylation does not impair proteasomal degradation but affects class I major histocompatibility complex presentation. 1795 Dec 57


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