Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.12.7.2 (hydrogenase)
 3,522 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In contrast to the widespread ability of bacteria, plants, and animals to incorporate selenium nonspecifically into proteins in the form of selenomethionine residues, the selenoamino acid selenocysteine occurs as a highly specific component of a few selenium-dependent enzymes. Selenocysteine has been identified in glycine reductase, formate dehydrogenase, and hydrogenase of bacterial origin and glutathione peroxidase from mammalian and avian sources. In these enzymes there is evidence that the selenol group, which is largely ionized at physiological pH, functions as a redox center. It now seems clear, from studies with both prokaryotes and eukaryotes, that the UGA opal stop codon is used to specify the cotranslational insertion of selenocysteine into proteins. The factors that allow this unusual use of the stop codon are, however, unknown. The occurrence of selenium as a normal constituent of several bacterial tRNA species has been established. The presence of a selenonucleoside, 5-methylaminomethyl-2-selenouridine, in the first or wobble position of the anticodons of certain glutamate and lysine iso-acceptor species influences codon-anticodon interaction and thus may serve to regulate translational processes. The biosynthesis of the selenonucleoside appears to involve the ATP-dependent activation of the sulfur in a preformed 5-methylaminomethyl-2-thiouridine residue in tRNA and replacement of the sulfur with selenium.
 ...
PMID:Specific occurrence of selenium in enzymes and amino acid tRNAs. 244 14

Selenocysteine is encoded by a UGA codon in all organisms that synthesise selenoproteins. This codon is specified as a selenocysteine codon by an mRNA secondary structure, which is located immediately 3' of the UGA in the reading frame of selenoprotein genes in Gram-negative bacteria, whereas it is located in the 3' untranslated region of eukaryal selenoprotein genes. The location and the structure of a similar mRNA signal in archaea has so far not been determined. Seven selenoproteins were identified for the archaeon Methanococcus jannaschii by labelling with 75Se and by SDS/polyacrylamide electrophoresis. Their size could be correlated with open reading frames possessing internal UGA codons from the total genomic sequence. One of the open reading frames, that of the VhuD subunit of a hydrogenase, possesses two UGA codons and appears to code for a selenoprotein with two selenocysteine residues. A strongly conserved mRNA element was identified that is exclusively linked to selenoprotein genes. It is located in the 3' untranslated region in six of the mRNAs and in the 5' untranslated region of the fdhA mRNA. This element, which is present in the 3' non-translated region of two selenoprotein mRNAs from Methanococcus voltae, is proposed to act in decoding of the UGA with selenocysteine.
 ...
PMID:Selenoprotein synthesis in archaea: identification of an mRNA element of Methanococcus jannaschii probably directing selenocysteine insertion. 910 56