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

---

Query: EC:6.3.2.19 (ubiquitin-protein ligase)
799 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Chromosome separation during the cell-cycle transition from metaphase to anaphase requires the proteolytic destruction of anaphase inhibitors such as Pds1 [1-3]. Proteolysis of Pds1 is mediated by a ubiquitin-protein ligase, the anaphase-promoting complex (APC) or cyclosome [4,5]. The APC is also necessary for the ubiquitin-dependent degradation of mitotic cyclins in late telophase as cells exit mitosis [6-9]. Although phosphorylation seems to be involved [10], it is not clear what activates the APC at the onset of anaphase. In Saccharomyces cerevisiae, chromosome segregation also requires the CDC20 gene, whose product contains WD40 repeats [11,12]. We have investigated the functional relationship between the APC and the Cdc20 protein. We present evidence that strongly suggests that Cdc20 is an essential regulator of APC-dependent proteolysis such that in the absence of Cdc20, cells are unable to degrade either Pds1 at the onset of anaphase or the mitotic cyclin Clb2 during telophase. This notion is consistent with our observations that Cdc20 is localized in the nucleus and co-immunoprecipitates with an APC component, Cdc23.
...
PMID:Cdc20 is essential for the cyclosome-mediated proteolysis of both Pds1 and Clb2 during M phase in budding yeast. 950 86

The yeast plasma membrane, uracil permease, undergoes ubiquitin-dependent endocytosis and subsequent degradation in the vacuole via a process that does not involve the proteasome. Cell-surface ubiquitination of this protein is mediated by the ubiquitin-protein ligase Npi1p/Rsp5p and involves Lys63-linked ubiquitin chains. This report describes the intracellular fate of a mutant form of uracil permease carrying a three amino acid insertion in a cytoplasmic loop. Most of this protein is not deployed beyond the ER, and is degraded by the 26S proteasome. Mutant permease degradation is almost unaffected in cells with impaired Npi1p/Rsp5p, but is dependent on the Ubc6p and Ubc7p ubiquitin-conjugating enzymes, suggesting that proteolysis of the protein requires its prior ubiquitination. Overproduction of a derivative of ubiquitin with a modified Lys48 strongly impairs mutant permease degradation. This suggests that, like other proteasome substrates, mutant permease might be polyubiquitinated with Lys48-linked ubiquitin chains. These findings provide an example of a yeast plasma membrane protein that is routed to the 'ER degradation' pathway, and highlight the versatility of the ubiquitin system.
...
PMID:'ER degradation' of a mutant yeast plasma membrane protein by the ubiquitin-proteasome pathway. 950 75

The RUB1/NEDD-8 family of ubiquitin-related genes is widely represented among eukaryotes. Here we report that Cdc53p in Saccharomyces cerevisiae, a member of the Cullin family of proteins, is stably modified by the covalent attachment of a single Rub1p molecule. Two genes have been identified that are required for Rub1p conjugation to Cdc53p. The first gene, designated ENR2, encodes a protein with sequence similarity to the amino-terminal half of the ubiquitin-activating enzyme. By analogy with Aos1p, we infer that Enr2p functions in a bipartite Rub1p-activating enzyme. The second gene is SKP1, shown previously to be required for some ubiquitin-conjugation events. A deletion allele of ENR2 is lethal with temperature-sensitive alleles of cdc34 and enhances the phenotypes of cdc4, cdc53, and skp1, strongly implying that Rub1p conjugation to Cdc53p is required for optimal assembly or function of the E3 complex SCFCdc4. Consistent with this model, both enr2delta and an allele of Cdc53p that is not Rub1p modified, render cells sensitive to alterations in the levels of Cdc4p, Cdc34p, and Cdc53p.
...
PMID:Modification of yeast Cdc53p by the ubiquitin-related protein rub1p affects function of the SCFCdc4 complex. 953 31

Ubiquitin conjugation is known to target protein substrates primarily to degradation by the proteasome or via the endocytic route. Here we describe a novel protein modification pathway in yeast which mediates the conjugation of RUB1, a ubiquitin-like protein displaying 53% amino acid identity to ubiquitin. We show that RUB1 conjugation requires at least three proteins in vivo. ULA1 and UBA3 are related to the N- and C-terminal domains of the E1 ubiquitin-activating enzyme, respectively, and together fulfil E1-like functions for RUB1 activation. RUB1 conjugation also requires UBC12, a protein related to E2 ubiquitin-conjugating enzymes, which functions analogously to E2 enzymes in RUB1-protein conjugate formation. Conjugation of RUB1 is not essential for normal cell growth and appears to be selective for a small set of substrates. Remarkably, CDC53/cullin, a common subunit of the multifunctional SCF ubiquitin ligase, was found to be a major substrate for RUB1 conjugation. This suggests that the RUB1 conjugation pathway is functionally affiliated to the ubiquitin-proteasome system and may play a regulatory role.
...
PMID:A novel protein modification pathway related to the ubiquitin system. 954 34

The hect domain protein family was originally identified by sequence similarity of its members to the C-terminal region of E6-AP, an E3 ubiquitin-protein ligase. Since the C terminus of E6-AP mediates thioester complex formation with ubiquitin, a necessary intermediate step in E6-AP-dependent ubiquitination, it was proposed that members of the hect domain family in general have E3 activity. The hect domain is approximately 350 amino acids in length, and we show here that the hect domain of E6-AP is necessary and sufficient for ubiquitin thioester adduct formation. Furthermore, the human genome encodes at least 20 different hect domain proteins, and in further support of the hypothesis that hect domain proteins represent a family of E3s, several of these are shown to form thioester complexes with ubiquitin. In addition, some hect domain proteins interact preferentially with UbcH5, whereas others interact with UbcH7, indicating that human hect domain proteins can be grouped into at least two classes based on their E2 specificity. Since E3s are thought to play a major role in substrate recognition, the presence of a large family of E3s should contribute to ensure the specificity and selectivity of ubiquitin-dependent proteolytic pathways.
...
PMID:Characterization of human hect domain family members and their interaction with UbcH5 and UbcH7. 957 61

The ubiquitin-proteasome pathway (UPP) regulates critical cell processes, including the cell cycle, cytokine-induced gene expression, differentiation, and cell death. Recently we demonstrated that this pathway responds to oxidative stress in mammalian cells and proposed that activities of ubiquitin-activating enzyme (E1) and ubiquitin-conjugating enzymes (E2s) are regulated by cellular redox status (i.e., GSSG:GSH ratio). To test this hypothesis, we altered the GSSG:GSH ratio in retinal pigment epithelial cells with the thiol-specific oxidant, diamide, and assessed activities of the UPP. Treatment of cells with diamide resulted in a dose-dependent increase in the GSSG:GSH ratio resulting from loss of GSH and a coincident increase in GSSG. Increases in the GSSG:GSH ratio from 0.02 in untreated cells to > or = 0.5 in diamide-treated cells were accompanied by dose-dependent reductions in the levels of endogenous Ub-protein conjugates, endogenous E1-ubiquitin thiol esters, and de novo ubiquitin-conjugating activity. As determined by the ability to form E1-ubiquitin and E2s-ubiquitin thiol esters, E1 and E2s were both inhibited by elevated GSSG:GSH ratios. Inhibition of E1 was associated with the formation of E1-protein mixed disulfides. Activities of E1 and E2s gradually recovered to preoxidation levels, coincident with gradual recovery of the GSSG:GSH ratio. These data support S-thiolation/dethiolation as a mechanism regulating E1 and E2 activities in response to oxidant insult. Ubiquitin-dependent proteolytic capacity was regulated by the GSSG:GSH ratio in a manner consistent with altered ubiquitin-conjugating activity. However, ubiquitin-independent proteolysis was unaffected by changes in the GSSG:GSH ratio. Potential adaptive and pathological consequences of redox regulation of UPP activities are discussed.
...
PMID:Redox regulation of ubiquitin-conjugating enzymes: mechanistic insights using the thiol-specific oxidant diamide. 957 83

Angelman syndrome (AS) is caused by chromosome 15q11-q13 deletions of maternal origin, by paternal uniparental disomy (UPD) 15, by imprinting defects, and by mutations in the UBE3A gene. UBE3A encodes a ubiquitin-protein ligase and shows brain-specific imprinting. Here we describe UBE3A coding-region mutations detected by SSCP analysis in 13 AS individuals or families. Two identical de novo 5-bp duplications in exon 16 were found. Among the other 11 unique mutations, 8 were small deletions or insertions predicted to cause frameshifts, 1 was a mutation to a stop codon, 1 was a missense mutation, and 1 was predicted to cause insertion of an isoleucine in the hect domain of the UBE3A protein, which functions in E2 binding and ubiquitin transfer. Eight of the cases were familial, and five were sporadic. In two familial cases and one sporadic case, mosaicism for UBE3A mutations was detected: in the mother of three AS sons, in the maternal grandfather of two AS first cousins, and in the mother of an AS daughter. The frequencies with which we detected mutations were 5 (14%) of 35 in sporadic cases and 8 (80%) of 10 in familial cases.
...
PMID:Mutation analysis of UBE3A in Angelman syndrome patients. 958 5

The onset of apoptosis is coupled to the proteolytic activation of a family of cysteine proteases, termed caspases. These proteases cleave their target proteins after an aspartate residue. Following caspase activation during apoptosis, a number of specific proteins have been shown to be cleaved. Here we show that Nedd4, a ubiquitin-protein ligase containing multiple WW domains and a calcium/lipid-binding domain, is also cleaved during apoptosis induced by a variety of stimuli including Fas-ligation, gamma-radiation, tumor necrosis factor-alpha, C-8 ceramide, and etoposide treatment. Extracts from apoptotic cells also generated cleavage patterns similar to that seen in vivo, and this cleavage was inhibited by an inhibitor of caspase-3-like proteases. In vitro, Nedd4 was cleaved by a number of caspases, including caspase-1, -3, -6, and -7. By site-directed mutagenesis, one of the in vitro caspase cleavage sites in mouse Nedd4 was mapped to a DQPD237 downward arrow sequence, which is conserved between mouse, rat, and human proteins. This is the first report demonstrating that an enzyme of the ubiquitin pathway is cleaved by caspases during apoptosis.
...
PMID:Caspase-mediated cleavage of the ubiquitin-protein ligase Nedd4 during apoptosis. 959 87

Epithelial Na+ channels are expressed widely in absorptive epithelia such as the renal collecting duct and the colon and play a critical role in fluid and electrolyte homeostasis. Recent studies have shown that these channels interact via PY motifs in the C terminals of their alpha, beta, and gamma subunits with the WW domains of the ubiquitin-protein ligase Nedd4. Mutation or deletion of these PY motifs (as occurs, for example, in the heritable form of hypertension known as Liddle's syndrome) leads to increased Na+ channel activity. Thus, binding of Nedd4 by the PY motifs would appear to be part of a physiological control system for down-regulation of Na+ channel activity. The nature of this control system is, however, unknown. In the present paper, we show that Nedd4 mediates the ubiquitin-dependent down-regulation of Na+ channel activity in response to increased intracellular Na+. We further show that Nedd4 operates downstream of Go in this feedback pathway. We find, however, that Nedd4 is not involved in the feedback control of Na+ channels by intracellular anions. Finally, we show that Nedd4 has no influence on Na+ channel activity when the Na+ and anion feedback systems are inactive. We conclude that Nedd4 normally mediates feedback control of epithelial Na+ channels by intracellular Na+, and we suggest that the increased Na+ channel activity observed in Liddle's syndrome is attributable to the loss of this regulatory feedback system.
...
PMID:Nedd4 mediates control of an epithelial Na+ channel in salivary duct cells by cytosolic Na+. 961 57

Recognition of substrate proteins by the ubiquitin-conjugation system is a highly specific and regulated event and involves the action of ubiquitin-conjugating enzymes (E2) and ubiquitin-protein ligases (E3). However, the E2 and E3 involved in the recognition of particular substrates have been identified in only a few cases. The ubiquitin-protein ligase E6-associated protein (E6-AP) was originally identified as a protein involved in the human papillomavirus E6-oncoprotein-induced degradation of p53. The substrate proteins of E6-AP in the absence of the E6 oncoprotein, however, have not been identified. We show here that E6-AP can target itself for ubiquitination in vitro and provide evidence that, under conditions of overexpression, E6-AP efficiently promotes its own degradation in vivo. Autoubiquitination of E6-AP is mediated mainly by intermolecular transfer of ubiquitin. In addition, highly ubiquitinated forms of E6-AP cannot bind to p53 in the presence of the E6 oncoprotein and, conversely, binding of E6-AP to p53 interferes with ubiquitination of E6-AP. These results suggest that autoubiquitination and subsequent degradation of E6-AP represents a mechanism to control intracellular E6-AP levels by inactivating E6-AP molecules that are not bound to substrate proteins.
...
PMID:The ubiquitin-protein ligase E6-associated protein (E6-AP) serves as its own substrate. 968 77


<< Previous 1 2 3 4 5 6 7 8 9 10

---