Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:6.1.1.12 (aspartyl-tRNA synthetase)
 233 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transfer RNAs from Escherichia coli, yeast (Sacharomyces cerevisiae), and calf liver were subjected to controlled hydrolysis with venom exonuclease to remove 3'-terminal nucleotides, and then reconstructed successively with cytosine triphosphate (CTP) and 2'- or 3'-deoxyadenosine 5'-triphosphate in the presence of yeast CTP(ATP):tRNA nucleotidyltransferase. The modified tRNAs were purified by chromatography on DBAE-cellulose or acetylated DBAE-cellulose and then utilized in tRNA aminoacylation experiments in the presence of the homologous aminoacyl-tRNA synthetase activities. The E. coli, yeast, and calf liver aminoacyl-tRNA synthetases specific for alanine, glycine, histidine, lysine, serine, and threonine, as well as the E. coli and yeast prolyl-tRNA synthetases and the yeast glutaminyl-tRNA synthetase utilized only those homologous modified tRNAs terminating in 2'-deoxyadenosine (i.e., having an available 3'-OH group). This is interpreted as evidence that these aminoacyl-tRNA synthetases normally aminoacylate their unmodified cognate tRNAs on the 3'-OH group. The aminoacyl-tRNA synthetases from all three sources specific argining, isoleucine, leucine, phenylalanine, and valine, as well as the E. coli and yeast enzymes specific for methionine and the E. coli glutamyl-tRNA synthetase, used as substrates exclusively those tRNAs terminating in 3'-deoxyadenosine. Certain aminoacyl-tRNA synthetases, including the E. coli, yeast, and calf liver asparagine and tyrosine activating enzymes, the E. coli and yeast cysteinyl-tRNA synthetases, and the aspartyl-tRNA synthetase from yeast, utilized both isomeric tRNAs as substrates, although generally not at the same rate. While the calf liver aspartyl- and cysteinyl-tRNA synthetases utilized only the corresponding modified tRNA species terminating in 2'-deoxyadenosine, the use of a more concentrated enzyme preparation might well result in aminoacylation of the isomeric species. The one tRNA for which positional specificity does seem to have changed during evolution is tryptophan, whose E. coli aminoacyl-tRNA synthetase utilized predominantly the cognate tRNA terminating in 3'-deoxyadenosine, while the corresponding yeast and calf liver enzymes were found to utilize predominantly the isomeric tRNAs terminating in 2'-deoxyadenosine. The data presented indicate that while there is considerable diversity in the initial position of aminoacylation of individual tRNA isoacceptors derived from a single source, positional specificity has generally been conserved during the evolution from a prokaryotic to mammalian organism.
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PMID:Initial position of aminoacylation of individual Escherichia coli, yeast, and calf liver transfer RNAs. 31 26

Transfer RNAs terminating 2'-or 3'-deoxyadenosine were prepared from unfractionated E. coli and yeast (Saccharomyces cerevisiae) tRNAs and purified to remove unmodified tRNAs. The modified tRNA species were assayed for aminoacylation with each of the 20 amino acids to determine the initial position of tRNA aminoacylation. The E. coli and yeast aminoacyl-tRNA synthetases specific for arginine, isoleucine, leucine, methionine, phenylalanine, and valine, as well as the E. coli glutamyl-tRNA synthetase, aminoacylated only those cognate tRNAs terminating in 3'-deoxyadenosine (i.e., those having a 2'-OH group). On the other hand, those E. coli and yeast synthetases specific for alanine, glycine, histidine, lysine, proline, serine, and threonine, as well as the yeast synthetase specific for glutamine, utilized exclusively those tRNAs having an available 3'-OH group on the 3'-terminal nucleoside, while the E. coli and yeast synthetases specific for asparagine, cysteine, and tyrosine, and the yeast aspartyl-tRNA synthetase, utilized both of the modified cognate tRNAs. The only observed difference in specificity between the E. coli and yeast systems was for tRNATrp, which was aminoacylated on the 2'-position in E. coli and the 3'-position in yeast. The results indicate that the initial position of aminoacylation is not uniform for all tRNAs, although for individual tRNAs the specificity has been conserved during the evolution from a prokaryotic to eukaryotic organism.
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PMID:Position of aminoacylation of individual Escherichia coli and yeast tRNAs. 110 23

The class-defining active site domain of the 10 class II tRNA synthetases is well conserved and, based on the crystal structure of aspartyl-tRNA synthetase, approaches the end of the tRNA acceptor stem from the major groove side of the helix. Paradoxically, for the class II alanyl-tRNA synthetase (AlaRS), aminoacylation is dependent on minor groove recognition of an acceptor helix G3.U70 base pair. Additional contributions to aminoacylation efficiency are made by the A73 "discriminator" base and G2.C71 base pair located at the end of the acceptor stem. Using microhelix substrates containing only the first four base pairs of the alanine tRNA acceptor helix, we demonstrated that the catalytic center of AlaRS with the three class-defining sequence motifs contains determinants for recognition of A73 and G2.C71. However, this structural unit does not discriminate between different base pairs at the critical 3.70 position. Discrimination at G3.U70 was mapped to a 76 amino acid polypeptide outside the catalytic center. We propose that the G3.U70 recognition motif is a structural appendage that folds back to the catalytic center to make contact with the bound acceptor stem. A "fold-back" appendage provides a specific mechanism for minor groove recognition of the acceptor helix by a class II tRNA synthetase.
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PMID:Minor groove recognition of the critical acceptor helix base pair by an appended module of a class II tRNA synthetase. 774 3

Crystallographic studies of the aspartyl-tRNA synthetase-tRNA(Asp)complex from yeast identified on the enzyme a number of residues potentially able to interact with tRNA(Asp). Alanine replacement of these residues (thought to disrupt the interactions) was used in the present study to evaluate their importance in tRNA(Asp)recognition and acylation. The results showed that contacts with the acceptor A of tRNA(Asp)by amino acid residues interacting through their side-chain occur only in the acylation transition state, whereas those located near the G73 discriminator base occur also during initial binding of tRNA(Asp). Interactions with the anticodon bases provide the largest free energy contribution to stability of the enzyme-tRNA complex in its ground state. These contacts also favour catalysis, by acting connectively with each other and with those of G73, as shown by multiple mutant analysis. This implies structural communication transmitting the anticodon recognition signal to the distally located acylation site. This signal might be conveyed via tRNA(Asp)as suggested by the observed conformational change of this molecule upon interaction with AspRS. From binding free energy values corresponding to the different AspRS-tRNA(Asp)interaction domains, it might be concluded that upon complex formation, the anticodon interacts first. Finally, acylation efficiencies of AspRS mutants in the presence of pure tRNA(Asp)and non-fractionated tRNAs indicate that residues involved in the binding of identity bases also discriminate against non-cognate tRNAs.
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PMID:Yeast aspartyl-tRNA synthetase residues interacting with tRNA(Asp) identity bases connectively contribute to tRNA(Asp) binding in the ground and transition-state complex and discriminate against non-cognate tRNAs. 1045 87

The heptapeptide-nucleotide microcin C (McC) is a potent inhibitor of enteric bacteria growth. Inside a sensitive cell, McC is processed by aminopeptidases, which release a nonhydrolyzable aspartyl-adenylate, a strong inhibitor of aspartyl-tRNA synthetase. The mccABCDE operon is sufficient for McC production and resistance of the producing cell to McC. An additional gene, mccF, which is adjacent to but not part of the mccABCDE operon, also provides resistance to exogenous McC. MccF is similar to Escherichia coli LdcA, an L,D-carboxypeptidase whose substrate is monomeric murotetrapeptide L-Ala-D-Glu-meso-A(2)pm-D-Ala or its UDP-activated murein precursor. The mechanism by which MccF provides McC resistance remained unknown. Here, we show that MccF detoxifies both intact and processed McC by cleaving an amide bond between the C-terminal aspartate and the nucleotide moiety. MccF also cleaves the same bond in nonhydrolyzable aminoacyl sulfamoyl adenosines containing aspartyl, glutamyl, and, to a lesser extent, seryl aminoacyl moieties but is ineffective against other aminoacyl adenylates.
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PMID:The mechanism of microcin C resistance provided by the MccF peptidase. 2087 30