Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.5.1.4 (deaminase)
 5,113 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The double-stranded RNA-specific editase 1 (RED1/ADAR2) is implicated in the editing of precursor-mRNAs (pre-mRNA) encoding subunits of glutamate receptors (GluRs) in brain. Site-specific deamination of adenosine to inosine alters the codon at the Q/R site in GluR-B rendering the heteromeric receptor impermeable to Ca2+ ions. We cloned human RED1 (hRED1/hADAR2) cDNAs from a brain cDNA library. The human enzyme is 95% identical to the rat homologue. We characterized two alternatively spliced forms that differed by the presence of an Alu-J cassette in the deaminase domain. For the long form containing the Alu cassette, we isolated cDNA clones with an alternative C-terminus and 3'-UTR. An 8.8-kb transcript of hRED1 is most abundant in brain and heart, and lower levels are detected in other tissues. In vitro editing assays with purified recombinant hRED1 containing or lacking the Alu-J cassette revealed that both forms of the protein have the same substrate specificity, but differ in their catalytic activity.
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PMID:Two forms of human double-stranded RNA-specific editase 1 (hRED1) generated by the insertion of an Alu cassette. 914 27

We have identified a homolog of the ADAR (adenosine deaminases that act on RNA) class of RNA editases from Drosophila, dADAR. The dADAR locus has been localized to the 2B6-7 region of the X chromosome and the complete genomic sequence organization is reported here. dADAR is most homologous to the mammalian RNA editing enzyme ADAR2, the enzyme that specifically edits the Q/R site in the pre-mRNA encoding the glutamate receptor subunit GluR-B. Partially purified dADAR expressed in Pichia pastoris has robust nonspecific A-to-I deaminase activity on synthetic dsRNA substrates. Transcripts of the dADAR locus originate from two regulated promoters. In addition, alternative splicing generates at least four major dADAR isoforms that differ at their amino-termini as well as altering the spacing between their dsRNA binding motifs. dADAR is expressed in the developing nervous system, making it a candidate for the editase that acts on para voltage-gated Na+ channel transcripts in the central nervous system. Surprisingly, dADAR itself undergoes developmentally regulated RNA editing that changes a conserved residue in the catalytic domain. Taken together, these findings show that both transcription and processing of dADAR transcripts are under strict developmental control and suggest that the process of RNA editing in Drosophila is dynamically regulated.
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PMID:dADAR, a Drosophila double-stranded RNA-specific adenosine deaminase is highly developmentally regulated and is itself a target for RNA editing. 1091 96

RNA editing catalyzed by ADAR1 and ADAR2 involves the site-specific conversion of adenosine to inosine within imperfectly duplexed RNA. ADAR1- and ADAR2-mediated editing occurs within transcripts of glutamate receptors (GluR) in the brain and in hepatitis delta virus (HDV) RNA in the liver. Although the Q/R site within the GluR-B premessage is edited more efficiently by ADAR2 than it is by ADAR1, the converse is true for the +60 site within this same transcript. ADAR1 and ADAR2 are homologs having two common functional regions, an N-terminal double-stranded RNA-binding domain and a C-terminal deaminase domain. It is neither understood why only certain adenosines within a substrate molecule serve as targets for ADARs, nor is it known which domain of an ADAR confers its specificity for particular editing sites. To assess the importance of several aspects of RNA sequence and structure on editing, we evaluated 20 different mutated substrates, derived from four editing sites, for their ability to be edited by either ADAR1 or ADAR2. We found that when these derivatives contained an A:C mismatch at the editing site, editing by both ADARs was enhanced compared to when A:A or A:G mismatches or A:U base pairs occurred at the same site. Hence substrate recognition and/or catalysis by ADARs could involve the base that opposes the edited adenosine. In addition, by using protein chimeras in which the deaminase domains were exchanged between ADAR1 and ADAR2, we found that this domain played a dominant role in defining the substrate specificity of the resulting enzyme.
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PMID:Substrate recognition by ADAR1 and ADAR2. 1142 61

One plausible hypothesis for selective neuronal death in sporadic amyotropic lateral sclerosis (ALS) is excitotoxicity mediated by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors, which are a subtype of ionotropic glutamate receptors. The Ca2+ conductance of AMPA receptors differs markedly depending on whether the GluR2 (or GluR-B) subunit is a component of the receptor. The properties of GluR2 are generated posttranscriptionally by RNA editing at the Q/R site in the putative second membrane domain (M2), during which the glutamine (Q) codon is substituted by an arginine (R) codon. AMPA receptors containing the unedited form of GluR2Q have high Ca2+ permeability in contrast to the low Ca2+ conductance of those containing the edited form of GluR2R. The role of Ca(2+)-permeable AMPA receptors, particularly GluR2 Q/R site RNA editing status, in neuronal death has been clearly demonstrated both in mice deficient in editing at the GluR2 Q/R site and in mice transgenic for an artificial Ca(2+)-permeable GluR2 subunit. We analyzed the expression level of mRNA of each AMPA receptor subunit in individual motor neurons, as well as the editing efficiency of GluR2 mRNA at the Q/R site in the single neuron level in control subjects and ALS cases. There was no significant difference as to the expression profile of AMPA receptor subunits or the proportion of GluR2 mRNA to total GluRs mRNA between normal subjects and ALS cases. By contrast, the editing efficiency varied greatly, from 0% to 100%, among the motor neurons of each individual with ALS, and was not complete in 44 of them (56%), whereas it remained 100% in normal controls. In addition, GluR2 editing efficiency was more than 99% in the cerebellar Purkinje cells of ALS, spinocerebellar degeneration and normal control groups. Thus, GluR2 underediting occurs in a disease specific and region selective manner. GluR2 modification by RNA editing is a biologically crucial event for neuronal survival, and its deficiency is a direct cause of neuronal death. Therefore, marked reduction of RNA editing in ALS motor neurons may be a direct cause of the selective motor neuron death seen in ALS. It is likely that the molecular mechanism underlying the deficiency in RNA editing is a reduction in the activity of ADAR2, a double- strand RNA specific deaminase. The restoration of this enzyme activity in ALS motor neurons may open the novel strategy for specific ALS therapy.
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PMID:Deficient RNA editing of GluR2 and neuronal death in amyotropic lateral sclerosis. 1562 11

Adenosine deaminases acting on RNA (ADARs) are best known for altering the coding sequences of mRNA through RNA editing, as in the GluR-B Q/R site. ADARs have also been shown to affect RNA interference (RNAi) and microRNA processing by deamination of specific adenosines to inosine. Here, we show that ADAR proteins can affect RNA processing independently of their enzymatic activity. We show that ADAR2 can modulate the processing of mir-376a2 independently of catalytic RNA editing activity. In addition, in a Drosophila assay for RNAi deaminase-inactive ADAR1 inhibits RNAi through the siRNA pathway. These results imply that ADAR1 and ADAR2 have biological functions as RNA-binding proteins that extend beyond editing per se and that even genomically encoded ADARs that are catalytically inactive may have such functions.
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PMID:Editing independent effects of ADARs on the miRNA/siRNA pathways. 1971 32