Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Twenty N-terminal point mutations of the human estrogen receptor (hER) were constructed as ubiquitin fusion products and expressed under the control of the copper regulated promoter CUP1 in Saccharomyces cerevisiae. The objective of these studies was to overexpress hER in yeast and also to evaluate the functional properties of the N-terminal variants of hER. Fusion of the C-terminus of ubiquitin to the N-terminus of other proteins has been shown to increase the level of protein expression in yeast. Ubiquitin C-terminal hydrolases (UCHs) in yeast efficiently and precisely cleave at the junction with ubiquitin and render free hER with desired amino termini. The variant hER proteins, that were generated by mutating the N-terminus of hER, showed enormous differences in receptor protein levels and transactivation potential. All variant hER proteins were synthesized as 66 kDa species as identified by Western blotting with the exception of the proline-containing variant (Pro-ER). The UB-Pro-ER variant was cleaved inefficiently by UCHs in yeast. The UB-Pro-hER [correction of UB-Pro-hEr] variant also exhibited a different DNA band-shift profile compared to those of the other receptor variants and the wild-type. Val-, Thr-, and Lys-ER did not express, as measured by enzyme-immunoassay and Western blotting; nor did they transactivate a beta-galactosidase reporter gene in yeast. However, the Glu-ER was 50% more active in transactivation as compared to the wild-type. The results of the receptor content, DNA binding properties and transactivation analysis in yeast demonstrate that the N-terminal residue plays an important role in the structure and function of hER.
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PMID:Structural and functional analysis of N-terminal point mutants of the human estrogen receptor. 863 65

Ubiquitin C-terminal hydrolases (UCH) are deubiquitinating enzymes which hydrolyze C-terminal esters and amides of ubiquitin. Here we report the processing of a number of ubiquitin derivatives by two human UCH isozymes (isozymes L1 and L3) and find that these enzymes show little discrimination based on the P1' amino acid, except that proline is cleaved slowly. Ubiquitinyllysine derivatives linked by the alpha- or epsilon-amino group are hydrolyzed at identical rates. Isozyme-specific hydrolytic preferences are only evident when the leaving group is large. The ubiquitin gene products can be cotranslationally processed by one or both of these UCH isozymes, and purified UbCEP52 can be hydrolyzed by UCH isozyme L3. Binding of nucleic acid by UbCEP52 converts it to a form resistant to processing by these enzymes, apparently because of the formation of a larger, more tightly folded substrate. Consistent with this postulate is the observation that these enzymes do not hydrolyze large ubiquitin derivatives such as N epsilon-ubiquitinyl-cytochrome-c, N epsilon-K48polyubiquitinyl-lysozyme, or an N alpha-ubiquitinyl-beta-galactosidase fusion protein. Thus, these enzymes rapidly and preferentially cleave small leaving groups such as amino acids and oligopeptides from the C-terminus of ubiquitin, but not larger leaving groups such as proteins. These data suggest that the physiological role of UCH is to hydrolyze small adducts of ubiquitin and to generate free monomeric ubiquitin from ubiquitin proproteins, but not to deubiquitinate ubiquitin-protein conjugates or disassemble polyubiquitin chains.
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PMID:Substrate specificity of deubiquitinating enzymes: ubiquitin C-terminal hydrolases. 952 56