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Histidyl-tRNA synthetase urzymes: Class I and II aminoacyl tRNA synthetase urzymes have comparable catalytic activities for cognate amino acid activation.

ABSTRACT: Four minimal (119-145 residue) active site fragments of Escherichia coli Class II histidyl-tRNA synthetase were constructed, expressed as maltose-binding protein fusions, and assayed for histidine activation as fusion proteins and after TEV cleavage, using the (32)PP(i) exchange assay. All contain conserved Motifs 1 and 2. Two contain an N-terminal extension of Motif 1 and two contain Motif 3. Five experimental results argue strongly for the authenticity of the observed catalytic activities: (i) active site titration experiments showing high (?0.1-0.55) fractions of active molecules, (ii) release of cryptic activity by TEV cleavage of the fusion proteins, (iii) reduced activity associated with an active site mutation, (iv) quantitative attribution of increased catalytic activity to the intrinsic effects of Motif 3, the N-terminal extension and their synergistic effect, and (v) significantly altered K(m) values for both ATP and histidine substrates. It is therefore plausible that neither the insertion domain nor Motif 3 were essential for catalytic activity in the earliest Class II aminoacyl-tRNA synthetases. The mean rate enhancement of all four cleaved constructs is ?10(9) times that of the estimated uncatalyzed rate. As observed for the tryptophanyl-tRNA synthetase (TrpRS) Urzyme, these fragments bind ATP tightly but have reduced affinity for cognate amino acids. These fragments thus likely represent Urzymes (Ur = primitive, original, earliest + enzyme) comparable in size and catalytic activity and coded by sequences proposed to be antisense to that coding the previously described Class I TrpRS Urzyme. Their catalytic activities provide metrics for experimental recapitulation of very early evolutionary events.

SUBMITTER: Li L

PROVIDER: S-EPMC3060492 | biostudies-literature | 2011 Mar

REPOSITORIES: biostudies-literature

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Histidyl-tRNA synthetase urzymes: Class I and II aminoacyl tRNA synthetase urzymes have comparable catalytic activities for cognate amino acid activation.

Li Li L Weinreb Violetta V Francklyn Christopher C Carter Charles W CW

The Journal of biological chemistry 20110126 12

Four minimal (119-145 residue) active site fragments of Escherichia coli Class II histidyl-tRNA synthetase were constructed, expressed as maltose-binding protein fusions, and assayed for histidine activation as fusion proteins and after TEV cleavage, using the (32)PP(i) exchange assay. All contain conserved Motifs 1 and 2. Two contain an N-terminal extension of Motif 1 and two contain Motif 3. Five experimental results argue strongly for the authenticity of the observed catalytic activities: (i) ...[more]

PMID: 21270472

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Project description:Tryptophanyl-tRNA synthetase (TrpRS) is a functionally dimeric ligase, which specifically couples hydrolysis of ATP to AMP and pyrophosphate to the formation of an ester bond between tryptophan and the cognate tRNA. TrpRS from Bacillus stearothermophilus binds the ATP analogue, adenosine-5' tetraphosphate (AQP) competitively with ATP during pyrophosphate exchange. Estimates of binding affinity from this competitive inhibition and from isothermal titration calorimetry show that AQP binds 200 times more tightly than ATP both under conditions of induced-fit, where binding is coupled to an unfavorable conformational change, and under exchange conditions, where there is no conformational change. These binding data provide an indirect experimental measurement of +3.0 kcal/mol for the conformational free energy change associated with induced-fit assembly of the active site. Thermodynamic parameters derived from the calorimetry reveal very modest enthalpic changes, consistent with binding driven largely by a favorable entropy change. The 2.5 A structure of the TrpRS:AQP complex, determined de novo by X-ray crystallography, resembles that of the previously described, pre-transition state TrpRS:ATP complexes. The anticodon-binding domain untwists relative to the Rossmann-fold domain by 20% of the way toward the orientation observed for the Products complex. An unexpected tetraphosphate conformation allows the gamma and deltad phosphate groups to occupy positions equivalent to those occupied by the beta and gamma phosphates of ATP. The beta-phosphate effects a 1.11 A extension that relocates the alpha-phosphate toward the tryptophan carboxylate while the PPi mimic moves deeper into the KMSKS loop. This configuration improves interactions between enzyme and nucleotide significantly and uniformly in the adenosine and PPi binding subsites. A new hydrogen bond forms between S194 from the class I KMSKS signature sequence and the PPi mimic. These complementary thermodynamic and structural data are all consistent with the conclusion that the tetraphosphate mimics a transition-state in which the KMSKS loop develops increasingly tight bonds to the PPi leaving group, weakening linkage to the Palpha as it is relocated by an energetically favorable domain movement. Consistent with extensive mutational data on Tyrosyl-tRNA synthetase, this aspect of the mechanism develops high transition-state affinity for the adenosine and pyrophosphate moieties, which move significantly, relative to one another, during the catalytic step.

Project description:BackgroundRecent studies point to a great diversity of non-ribosomal peptide synthesis systems with major roles in amino acid and co-factor biosynthesis, secondary metabolism, and post-translational modifications of proteins by peptide tags. The least studied of these systems are those utilizing tRNAs or aminoacyl-tRNA synthetases (AAtRS) in non-ribosomal peptide ligation.ResultsHere we describe novel examples of AAtRS related proteins that are likely to be involved in the synthesis of widely distributed peptide-derived metabolites. Using sensitive sequence profile methods we show that the cyclodipeptide synthases (CDPSs) are members of the HUP class of Rossmannoid domains and are likely to be highly derived versions of the class-I AAtRS catalytic domains. We also identify the first eukaryotic CDPSs in fungi and in animals; they might be involved in immune response in the latter organisms. We also identify a paralogous version of the methionyl-tRNA synthetase, which is widespread in bacteria, and present evidence using contextual information that it might function independently of protein synthesis as a peptide ligase in the formation of a peptide- derived secondary metabolite. This metabolite is likely to be heavily modified through multiple reactions catalyzed by a metal-binding cupin domain and a lysine N6 monooxygenase that are strictly associated with this paralogous methionyl-tRNA synthetase (MtRS). We further identify an analogous system wherein the MtRS has been replaced by more typical peptide ligases with the ATP-grasp or modular condensation-domains.ConclusionsThe prevalence of these predicted biosynthetic pathways in phylogenetically distant, pathogenic or symbiotic bacteria suggests that metabolites synthesized by them might participate in interactions with the host. More generally, these findings point to a complete spectrum of recruitment of AAtRS to various non-ribosomal biosynthetic pathways, ranging from the conventional AAtRS, through closely related paralogous AAtRS dedicated to certain pathways, to highly derived versions of the class-I AAtRS catalytic domain like the CDPSs. Both the conventional AAtRS and their closely related paralogs often provide aminoacylated tRNAs for peptide ligations by MprF/Fem/MurM-type acetyltransferase fold ligases in the synthesis of peptidoglycan, N-end rule modifications of proteins, lipid aminoacylation or biosynthesis of antibiotics, such as valinamycin. Alternatively they might supply aminoacylated tRNAs for other biosynthetic pathways like that for tetrapyrrole or directly function as peptide ligases as in the case of mycothiol and those identified here.

Project description:MotivationSimilarities in core residue packing provide evidence for divergence or convergence not reported using other methods.ResultsWe apply a new method for rapid structure comparison based on Simplicial Neighborhood Analysis of Protein Packing (SNAPP) to the diverse structural classification of proteins (SCOP) alpha/beta-class of protein folds. The procedure identifies inter-residue packing motifs shared by protein pairs from different folds. A threshold of 0.67 A RMSD for all atoms of corresponding residues ensures inclusion of only highly significant similarities comparable with those observed for identical catalytic residues in homologues. Many tertiary packing motifs are shared among the three classical Rossmannoid folds, as well as thousands of other motifs that occur in at least two distinct folds. Merging of neighboring packing motifs facilitated recognition of larger, recurrent substructures or cores. The anti-codon-binding domain of an archeal aminoacyl-tRNA synthetase (aaRS) was discovered to possess a packed core in which eight identical amino acid residues are within 0.55 A RMSD of the comparable structure in the FixJ receiver, a member of the Rossmannoid family that also includes the CheY signaling protein and flavodoxin-like proteins. Further investigation identified close variants of this core in five other Rossmannoid folds, including a functionally relevant core in Class Ia aminoacyl-tRNA synthetases. Although it is possible that the two essentially identical cores in the ProRS anti-codon-binding domain and the FixJ receiver converged to the same structure, the consensus core obtained from the structural and sequence alignments suggests that all the implicated protein folds descended from a simpler ancestral protein in which this core provided nucleotide binding and proto-allosteric functions.AvailabilityPrograms are available at http://staff.vbi.vt.edu/cammer/snapp/download/ImplementationPrograms were written in Perl and c and run under Linux.Contactcammer@vbi.vt.edu.

Dataset Information

Histidyl-tRNA synthetase urzymes: Class I and II aminoacyl tRNA synthetase urzymes have comparable catalytic activities for cognate amino acid activation.

Publications

Histidyl-tRNA synthetase urzymes: Class I and II aminoacyl tRNA synthetase urzymes have comparable catalytic activities for cognate amino acid activation.

Similar Datasets

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