共查询到20条相似文献，搜索用时 39 毫秒
1.
The mechanisms that determine how folding attempts are interrupted to target folding-incompetent proteins for endoplasmic reticulum-associated degradation (ERAD) are poorly defined. Here the alpha-mannosidase I-like protein EDEM was shown to extract misfolded glycoproteins, but not glycoproteins undergoing productive folding, from the calnexin cycle. EDEM overexpression resulted in faster release of folding-incompetent proteins from the calnexin cycle and earlier onset of degradation, whereas EDEM down-regulation prolonged folding attempts and delayed ERAD. Up-regulation of EDEM during ER stress may promote cell recovery by clearing the calnexin cycle and by accelerating ERAD of terminally misfolded polypeptides. 相似文献
2.
Ushioda R Hoseki J Araki K Jansen G Thomas DY Nagata K 《Science (New York, N.Y.)》2008,321(5888):569-572
Membrane and secretory proteins cotranslationally enter and are folded in the endoplasmic reticulum (ER). Misfolded or unassembled proteins are discarded by a process known as ER-associated degradation (ERAD), which involves their retrotranslocation into the cytosol. ERAD substrates frequently contain disulfide bonds that must be cleaved before their retrotranslocation. Here, we found that an ER-resident protein ERdj5 had a reductase activity, cleaved the disulfide bonds of misfolded proteins, and accelerated ERAD through its physical and functional associations with EDEM (ER degradation-enhancing alpha-mannosidase-like protein) and an ER-resident chaperone BiP. Thus, ERdj5 is a member of a supramolecular ERAD complex that recognizes and unfolds misfolded proteins for their efficient retrotranslocation. 相似文献
3.
Some nascent proteins that fold within the endoplasmic reticulum (ER) never reach their native state. Misfolded proteins are removed from the folding machinery, dislocated from the ER into the cytosol, and degraded in a series of pathways collectively referred to as ER-associated degradation (ERAD). Distinct ERAD pathways centered on different E3 ubiquitin ligases survey the range of potential substrates. We now know many of the components of the ERAD machinery and pathways used to detect substrates and target them for degradation. Much less is known about the features used to identify terminally misfolded conformations and the broader role of these pathways in regulating protein half-lives. 相似文献
4.
【目的】在植物中,内质网胁迫（endoplasmic reticulum stress,ERS）和未折叠蛋白应答（unfolded protein response,UPR）参与环境胁迫响应过程,然而,玉米种子老化过程中内质网胁迫相关基因表达情况尚未见报道。文章利用基因数字表达谱技术探究玉米种子老化过程中内质网胁迫相关基因表达规律,以期为揭示种子衰老的分子机制提供理论依据。【方法】以玉米杂交种郑单958种子为材料,采用高温（45℃）高湿（相对湿度100%）的方法进行人工老化处理。分别提取未老化处理（对照）和老化处理3 d的玉米种胚总RNA,利用Illumina HiSeqTM 2000平台进行高通量测序。去除原始数据中的接头序列、包含模糊碱基的序列以及低质量序列,获得Clean reads,利用短序列比对软件SOAPaligner/ SOAP2将Clean Reads分别比对到玉米参考基因组和参考基因序列,采用RPKM（reads per kb per million reads）方法计算基因的表达量,根据FDR（false discovery rate）＜0.001和|log2 ratio(T/CK)|≥1的标准筛选差异表达的基因,对获得的差异表达基因（differentially expressed genes,DEGs）进行KEGG（kyoto encyclopedia of genes and genomes）数据库功能注释分析,筛选出响应人工老化的内质网胁迫相关差异表达基因。利用qRT-PCR技术定量分析内质网胁迫相关基因在不同人工老化时间内的表达特性。【结果】基因数字表达谱鉴定结果表明,有104个差异表达基因在人工老化过程中参与内质网蛋白质加工（protein processing in endoplasmic reticulum）通路,其中内质网胁迫相关基因有97个（81个上调表达,16个下调表达）。对差异表达基因功能注释分析表明,内质网胁迫的标志性蛋白基因BiP以及分子伴侣蛋白基因CRT、CNT和GRP94等显著上调表达。参与内质网相关性降解（endoplasmic reticulum-associated degradation,ERAD）途径的有83个差异表达基因（70个上调,13个下调）,其中启动ERAD途径的关键酶基因EDEM （ER degradation enhancing mannosidase I-like protein）下调,参与蛋白泛素化的E2泛素结合酶基因UbcH5、E3泛素连接酶基因Hrd1和Doa10等也发生显著的表达变化。qRT-PCR结果表明,内质网胁迫相关基因在不同人工老化时间内表现表达多样性和复杂性。【结论】人工老化处理能造成玉米种胚细胞发生内质网胁迫。细胞通过上调分子伴侣基因表达和诱导ERAD途径响应内质网胁迫,但ERAD途径受阻可能引起错误折叠蛋白聚集,从而进一步加剧细胞损伤,最终导致种子活力降低甚至丧失。 相似文献
5.
6.
7.
概述了蛋白质品质管理中涉及的分子伴侣、激发未折叠蛋白反应(unfolded protein response, UPR)和内质网相关性蛋白质降解途径(ER-associated degradation, ERAD)等的研究进展,并探讨了该领域存在的问题以及发展前景。指出蛋白质的生命过程经历生成、折叠、组装和降解,每个过程都有严格控制。内质网中,各种蛋白质合成、折叠并经修饰形成具有一定构象的功能性蛋白。其在内质网折叠受阻碍时,未折叠的蛋白聚集,激发 UPR,使一系列分子伴侣和蛋白质折叠所需修饰酶类表达上调,帮助其完成折叠和装配。如果这些蛋白仍不能正确折叠,则进入 ERAD 被降解。 相似文献
8.
概述了蛋白质品质管理中涉及的分子伴侣、激发未折叠蛋白反应(unfolded protein response,UPR)和内质网相关性蛋白质降解途径(ER-associated degradation,ERAD)等的研究进展,并探讨了该领域存在的问题以及发展前景。指出蛋白质的生命过程经历生成、折叠、组装和降解,每个过程都有严格控制。内质网中,各种蛋白质合成、折叠并经修饰形成具有一定构象的功能性蛋白。其在内质网折叠受阻碍时,未折叠的蛋白聚集,激发UPR,使一系列分子伴侣和蛋白质折叠所需修饰酶类表达上调,帮助其完成折叠和装配。如果这些蛋白仍不能正确折叠,则进入ERAD被降解。 相似文献
9.
Nascent polypeptides emerging from the ribosome and not yet folded may at least transiently present degradation signals similar to those recognized by the ubiquitin system in misfolded proteins. The ubiquitin sandwich technique was used to detect and measure cotranslational protein degradation in living cells. More than 50 percent of nascent protein molecules bearing an amino-terminal degradation signal can be degraded cotranslationally, never reaching their mature size before their destruction by processive proteolysis. Thus, the folding of nascent proteins, including abnormal ones, may be in kinetic competition with pathways that target these proteins for degradation cotranslationally. 相似文献
10.
Changes in prion protein (PrP) folding are associated with fatal neurodegenerative disorders, but the neurotoxic species is unknown. Like other proteins that traffic through the endoplasmic reticulum, misfolded PrP is retrograde transported to the cytosol for degradation by proteasomes. Accumulation of even small amounts of cytosolic PrP was strongly neurotoxic in cultured cells and transgenic mice. Mice developed normally but acquired severe ataxia, with cerebellar degeneration and gliosis. This establishes a mechanism for converting wild-type PrP to a highly neurotoxic species that is distinct from the self-propagating PrP(Sc) isoform and suggests a potential common framework for seemingly diverse PrP neurodegenerative disorders. 相似文献
11.
A peptide sequence confers retention and rapid degradation in the endoplasmic reticulum 总被引：32，自引：0，他引：32
A nonlysosomal pathway exists for the degradation of newly synthesized proteins retained within the endoplasmic reticulum (ER). This pathway is extremely selective: whereas some proteins are rapidly degraded, others survive for long periods in the ER. The question of whether this selectivity is due to the presence within the sensitive proteins of definable peptide sequences that are sufficient to target them for degradation has been addressed. Deletion of a carboxyl-terminal sequence, comprising the transmembrane domain and short cytoplasmic tail of the alpha chain of the T cell antigen receptor (TCR-alpha), prevented the rapid degradation of this polypeptide. Fusion of this carboxyl-terminal sequence to the extracellular domain of the Tac antigen, a protein that is normally transported to the cell surface where it survives long-term, resulted in the retention and rapid degradation of the chimeric protein in the ER. Additional mutagenesis revealed that the transmembrane domain of TCR-alpha alone was sufficient to cause degradation within the ER. This degradation was not a direct consequence of retention in the ER, as blocking transport of newly synthesized proteins out of the ER with brefeldin A did not lead to degradation of the normal Tac antigen. It is proposed that a 23-amino acid sequence, comprising the transmembrane domain of TCR-alpha, contains information that determines targeting for degradation within the ER system. 相似文献
12.
Uncoupling translocation from translation: implications for transport of proteins across membranes 总被引：42，自引：0，他引：42
The segregation of secretory proteins into the cisternae of the endoplasmic reticulum (ER) is normally tightly coupled to their synthesis. This feature distinguishes their biogenesis from that of proteins targeted to many other organelles. In the examples presented, translocation across the ER membrane is dissociated from translation. Transport, which is normally cotranslational, may proceed in the absence of chain elongation. Moreover, translocation across the ER membrane does not proceed spontaneously since, even in the absence of protein synthesis, energy substrates are required for translocation. These conclusions have been extended to the cotranslational integration of newly synthesized transmembrane proteins. 相似文献
13.
Plant development: regulation by protein degradation 总被引：2，自引：0，他引：2
Many aspects of eukaryotic development depend on regulated protein degradation by the ubiquitin-proteasome pathway. This highly conserved pathway promotes covalent attachment of ubiquitin to protein substrates through the sequential action of three enzymes called a ubiquitin-activating enzyme (E1), a ubiquitin-conjugating enzyme (E2), and a ubiquitin-protein ligase (E3). Most ubiquitinated proteins are then targeted for degradation by the 26S proteasome. Recent studies have also shown that the ubiquitin-related protein RUB/Nedd8 and the proteasome-related COP9 signalosome complex cooperate with the ubiquitin-proteasome pathway to promote protein degradation. Most of these components are conserved in all three eukaryotic kingdoms. However, the known targets of the pathway in plants, and the developmental processes they regulate, are specific to the plant kingdom. 相似文献
14.
Hetz C Bernasconi P Fisher J Lee AH Bassik MC Antonsson B Brandt GS Iwakoshi NN Schinzel A Glimcher LH Korsmeyer SJ 《Science (New York, N.Y.)》2006,312(5773):572-576
Accumulation of misfolded protein in the endoplasmic reticulum (ER) triggers an adaptive stress response-termed the unfolded protein response (UPR)-mediated by the ER transmembrane protein kinase and endoribonuclease inositol-requiring enzyme-1alpha (IRE1alpha). We investigated UPR signaling events in mice in the absence of the proapoptotic BCL-2 family members BAX and BAK [double knockout (DKO)]. DKO mice responded abnormally to tunicamycin-induced ER stress in the liver, with extensive tissue damage and decreased expression of the IRE1 substrate X-box-binding protein 1 and its target genes. ER-stressed DKO cells showed deficient IRE1alpha signaling. BAX and BAK formed a protein complex with the cytosolic domain of IRE1alpha that was essential for IRE1alpha activation. Thus, BAX and BAK function at the ER membrane to activate IRE1alpha signaling and to provide a physical link between members of the core apoptotic pathway and the UPR. 相似文献
15.
Lin JH Li H Yasumura D Cohen HR Zhang C Panning B Shokat KM Lavail MM Walter P 《Science (New York, N.Y.)》2007,318(5852):944-949
16.
Scorrano L Oakes SA Opferman JT Cheng EH Sorcinelli MD Pozzan T Korsmeyer SJ 《Science (New York, N.Y.)》2003,300(5616):135-139
BAX and BAK are "multidomain" proapoptotic proteins that initiate mitochondrial dysfunction but also localize to the endoplasmic reticulum (ER). Mouse embryonic fibroblasts deficient for BAX and BAK (DKO cells) were found to have a reduced resting concentration of calcium in the ER ([Ca2+]er) that results in decreased uptake of Ca2+ by mitochondria after Ca2+ release from the ER. Expression of SERCA (sarcoplasmic-endoplasmic reticulum Ca2+ adenosine triphosphatase) corrected [Ca2+]er and mitochondrial Ca2+ uptake in DKO cells, restoring apoptotic death in response to agents that release Ca2+ from intracellular stores (such as arachidonic acid, C2-ceramide, and oxidative stress). In contrast, targeting of BAX to mitochondria selectively restored apoptosis to "BH3-only" signals. A third set of stimuli, including many intrinsic signals, required both ER-released Ca2+ and the presence of mitochondrial BAX or BAK to fully restore apoptosis. Thus, BAX and BAK operate in both the ER and mitochondria as an essential gateway for selected apoptotic signals. 相似文献
17.
Role of Rpn11 metalloprotease in deubiquitination and degradation by the 26S proteasome 总被引：1，自引：0，他引：1
Verma R Aravind L Oania R McDonald WH Yates JR Koonin EV Deshaies RJ 《Science (New York, N.Y.)》2002,298(5593):611-615
The 26S proteasome mediates degradation of ubiquitin-conjugated proteins. Although ubiquitin is recycled from proteasome substrates, the molecular basis of deubiquitination at the proteasome and its relation to substrate degradation remain unknown. The Rpn11 subunit of the proteasome lid subcomplex contains a highly conserved Jab1/MPN domain-associated metalloisopeptidase (JAMM) motif-EX(n)HXHX(10)D. Mutation of the predicted active-site histidines to alanine (rpn11AXA) was lethal and stabilized ubiquitin pathway substrates in yeast. Rpn11(AXA) mutant proteasomes assembled normally but failed to either deubiquitinate or degrade ubiquitinated Sic1 in vitro. Our findings reveal an unexpected coupling between substrate deubiquitination and degradation and suggest a unifying rationale for the presence of the lid in eukaryotic proteasomes. 相似文献
18.
A free NH2-terminal group has been previously shown to be an obligatory signal for recognition and subsequent degradation of proteins in a partially fractionated and reconstituted ubiquitin proteolytic system. Naturally occurring proteins with acetylated NH2-termini--most cellular proteins fall in this category--were not degraded by this system. Other studies have suggested that the identity of the NH2-terminal residue is important in determining the metabolic stability of a protein in vivo (N-end rule). Whole reticulocyte lysate and antibodies directed against the ubiquitin-activating enzyme (E1) have now been used to show that such acetylated proteins are degraded in a ubiquitin-dependent mode. Although fractionation of lysate does not affect its proteolytic activity toward substrates with free NH2-termini, it completely abolishes the activity toward the blocked substrates, indicating that an important component of the system was either removed or inactivated during fractionation. An NH2-terminal "unblocking" activity that removes the blocking group, thus exposing a free NH2-terminus for recognition according to the N-end rule, does not seem to participate in this pathway. Incubation of whole lysate with labeled histone H2A results in the formation of multiple ubiquitin conjugates. In contrast, the fractionated system is devoid of any significant conjugating activity. These results suggest that a novel conjugating enzyme (possibly a ubiquitin-protein ligase) may be responsible for the degradation of these acetylated proteins by recognizing structural features of the substrate that are downstream and distinct from the NH2-terminal residue. 相似文献
19.
Pearce MJ Mintseris J Ferreyra J Gygi SP Darwin KH 《Science (New York, N.Y.)》2008,322(5904):1104-1107
The protein modifier ubiquitin is a signal for proteasome-mediated degradation in eukaryotes. Proteasome-bearing prokaryotes have been thought to degrade proteins via a ubiquitin-independent pathway. We have identified a prokaryotic ubiquitin-like protein, Pup (Rv2111c), which was specifically conjugated to proteasome substrates in the pathogen Mycobacterium tuberculosis. Pupylation occurred on lysines and required proteasome accessory factor A (PafA). In a pafA mutant, pupylated proteins were absent and substrates accumulated, thereby connecting pupylation with degradation. Although analogous to ubiquitylation, pupylation appears to proceed by a different chemistry. Thus, like eukaryotes, bacteria may use a small-protein modifier to control protein stability. 相似文献
20.
The vast majority of proteins that a cell secretes or displays on its surface first enter the endoplasmic reticulum (ER), where they fold and assemble. Only properly assembled proteins advance from the ER to the cell surface. To ascertain fidelity in protein folding, cells regulate the protein-folding capacity in the ER according to need. The ER responds to the burden of unfolded proteins in its lumen (ER stress) by activating intracellular signal transduction pathways, collectively termed the unfolded protein response (UPR). Together, at least three mechanistically distinct branches of the UPR regulate the expression of numerous genes that maintain homeostasis in the ER or induce apoptosis if ER stress remains unmitigated. Recent advances shed light on mechanistic complexities and on the role of the UPR in numerous diseases. 相似文献