Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P62988 (Ubiquitin)
 4,326 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ubiquitin-mediated protein modification via covalent attachment of ubiquitin has emerged as one of the most common regulatory processes in all eukaryotes. Nedd4-2, closely related to neuronal precursor cell-expressed developmentally down-regulated 4 (Nedd4), is a multimodular ubiquitin-protein ligase comprised of four WW domains and a Hect domain. The WW domains recognize the proline-rich motifs on the multi-subunit amiloride-sensitive epithelial sodium channel (ENaC). To gain insights into the binding of the WW domain to proline-rich peptides, a protein fragment (78 amino acids) containing the fourth WW domain (WW4) of the Nedd4-2 protein was purified and crystallized and X-ray diffraction data were collected. A data set was obtained to 2.5 A resolution from a cryocooled single crystal at a synchrotron source. The crystals belong to the tetragonal space group P4(1)2(1)2 (or P4(3)2(1)2), with unit-cell parameters a = b = 113.43, c = 103.21 A. Analysis of the self-rotation function suggests the presence of four WW4 molecules in the asymmetric unit, with a high unit-cell solvent content of 74%.
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PMID:Crystallization and preliminary X-ray diffraction studies of the WW4 domain of the Nedd4-2 ubiquitin-protein ligase. 1651 Dec 41

Serum- and glucocorticoid-induced protein kinase-1 (SGK-1) plays a critical role in regulation of the epithelial sodium channel, ENaC. SGK-1 also shares significant catalytic domain homology with protein kinase B (PKB/AKT-1) and is a downstream effector of antiapoptotic phosphoinositide 3-kinase signaling. Steady-state levels of an active SGK-1 are tightly regulated by rapid transcriptional activation and post-translational modification including phosphorylation. We show here that endogenous SGK-1 protein is polyubiquitinated and rapidly degraded by the 26S proteasome. In contrast to other rapidly degraded kinases, neither the catalytic activity of SGK-1 nor activation site phosphorylation was required for its ubiquitin modification and degradation. Instead, SGK-1 degradation required a lysine-less six-amino-acid (amino acids 19-24) hydrophobic motif (GMVAIL) within the N-terminal domain. Deletion of amino acids 19-24 significantly increased the half-life of SGK1 and prevented its ubiquitin modification. Interestingly, this minimal region was also required for the association of SGK-1 with the endoplasmic reticulum. Ubiquitin modification and degradation of SGK-1 were increasingly inhibited by the progressive mutation of six N-terminal lysine residues surrounding the GMVAIL motif. Mutation of all six lysines to arginine did not disrupt the subcellular localization of SGK-1 despite a significant decrease in ubiquitination, implying that this modification per se was not required for targeting to the endoplasmic reticulum. These results suggest that constitutive ubiquitin-mediated degradation of SGK-1 is an important mechanism regulating its biological activity.
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PMID:A novel N-terminal hydrophobic motif mediates constitutive degradation of serum- and glucocorticoid-induced kinase-1 by the ubiquitin-proteasome pathway. 1681 52

Ubiquitin ligases play a pivotal role in substrate recognition and ubiquitin transfer, yet little is known about the regulation of their catalytic activity. Nedd4 (neural-precursor-cell-expressed, developmentally down-regulated 4)-2 is an E3 ubiquitin ligase composed of a C2 domain, four WW domains (protein-protein interaction domains containing two conserved tryptophan residues) that bind PY motifs (L/PPXY) and a ubiquitin ligase HECT (homologous with E6-associated protein C-terminus) domain. In the present paper we show that the WW domains of Nedd4-2 bind (weakly) to a PY motif (LPXY) located within its own HECT domain and inhibit auto-ubiquitination. Pulse-chase experiments demonstrated that mutation of the HECT PY-motif decreases the stability of Nedd4-2, suggesting that it is involved in stabilization of this E3 ligase. Interestingly, the HECT PY-motif mutation does not affect ubiquitination or down-regulation of a known Nedd4-2 substrate, ENaC (epithelial sodium channel). ENaC ubiquitination, in turn, appears to promote Nedd4-2 self-ubiquitination. These results support a model in which the inter- or intra-molecular WW-domain-HECT PY-motif interaction stabilizes Nedd4-2 by preventing self-ubiquitination. Substrate binding disrupts this interaction, allowing self-ubiquitination of Nedd4-2 and subsequent degradation, resulting in down-regulation of Nedd4-2 once it has ubiquitinated its target. These findings also point to a novel mechanism employed by a ubiquitin ligase to regulate itself differentially compared with substrate ubiquitination and stability.
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PMID:Regulation of Nedd4-2 self-ubiquitination and stability by a PY motif located within its HECT-domain. 1849 46

Amiloride-sensitive epithelial sodium (Na(+)) channels (ENaC) play a crucial role in Na(+) transport and fluid reabsorption in the kidney, lung, and colon. The magnitude of ENaC-mediated Na(+) transport in epithelial cells depends on the average open probability of the channels and the number of channels on the apical surface of epithelial cells. The number of channels in the apical membrane, in turn, depends upon a balance between the rate of ENaC insertion and the rate of removal from the apical membrane. ENaC is made up of three homologous subunits, alpha, beta, and gamma. The C-terminal domain of all three subunits is intracellular and contains a proline rich motif (PPxY). Mutations or deletion of this PPxY motif in the beta and gamma subunits prevent the binding of one isoform of a specific ubiquitin ligase, neural precursor cell expressed developmentally down-regulated protein (Nedd4-2) to the channel in vitro and in transfected cell systems, thereby impeding ubiquitin conjugation of the channel subunits. Ubiquitin conjugation would seem to imply that ENaC turnover is determined by the ubiquitin-proteasome system, but when MDCK cells are transfected with ENaC, ubiquitin conjugation apparently leads to lysosomal degradation. However, in untransfected epithelial cells (A6) expressing endogenous ENaC, ENaC appears to be degraded by the ubiquitin-proteasome system. Nonetheless, in both transfected and untransfected cells, the rate of ENaC degradation is apparently controlled by the rate of Nedd4-2-mediated ENaC ubiquitination. Controlling the rate of degradation is apparently important enough to have multiple, redundant pathways to control Nedd4-2 and ENaC ubiquitination.
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PMID:Regulation of epithelial sodium channel trafficking by ubiquitination. 2016 Jan 49