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-dependent proteolysis is a major proteolytic pathway in the cytoplasm and nucleus of eukaryotic cells. We introduced a gene encoding a substrate for this pathway into the genome of Arabidopsis thaliana. The transgene codes for a hybrid protein consisting of dihydrofolate reductase (DHFR, EC 1.5.1.3) fused to a degradation signal that is specifically recognized by components of the ubiquitin-dependent proteolysis pathway. Elevated concentrations of the DHFR protein confer resistance to the drug methotrexate, but rapid degradation prevents accumulation of the protein in the plant. Therefore, transgenic A. thaliana lines expressing the DHFR fusion protein are methotrexate-sensitive. Selection for mutants resistant to methotrexate resulted in plants impaired in degradation of the DHFR model substrate, as shown by an increase in protein level in the mutants.
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PMID:Use of a reporter transgene to generate arabidopsis mutants in ubiquitin-dependent protein degradation. 1160 48

PA700, the 19 S regulatory complex of the 26 S proteasome, plays a central role in the recognition and efficient degradation of misfolded proteins. PA700 promotes degradation by recruiting proteasomal substrates utilizing polyubiquitin chains and chaperone-like binding activities and by opening the access to the core of the 20 S proteasome to promote degradation. Here we provide evidence that PA700 in addition to binding misfolded protein substrates also acts to remodel their conformation prior to proteolysis. Scrambled RNase A (scRNase A), a misfolded protein, only slowly refolds spontaneously into an active form because of the rate-limiting unfolding of misfolded disulfide isomers. Notably, PA700 accelerates the rate of reactivation of scRNase A, consistent with its ability to increase the exposure of these disulfide bonds to the solvent. In this regard, PA700 also exposes otherwise buried sites to digestion by exogenous chymotrypsin in a polyubiquitinated enzymatically active substrate, pentaubiquitinated dihydrofolate reductase, Ub(5)DHFR. The dihydrofolate reductase ligand methotrexate counters the ability of PA700 to promote digestion by chymotrypsin. Together, these results indicate that in addition to increasing substrate affinity and opening the access channel to the catalytic sites, PA700 activates proteasomal degradation by remodeling the conformation of protein substrates.
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PMID:Conformational remodeling of proteasomal substrates by PA700, the 19 S regulatory complex of the 26 S proteasome. 1201 Oct 44

The importance of substrate polyubiquitination in protein degradation has been established for many years. However, the many intricacies of substrate recognition and ubiquitination by E3 enzymes have greatly limited access to degradable substrate in vitro. Thus, detailed analysis of protein degradation using purified 26S proteasomes has been difficult. The ability to synthesize polyubiquitin chains in a test tube has provided a method to make large quantities of a specific polyubiquitinated substrate, Ub(5)DHFR. This chapter focuses on the synthesis and degradation of this model substrate.
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PMID:The synthesis and proteasomal degradation of a model substrate Ub5DHFR. 1627 44