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Richard Giegé

Publications and source records attributed to Richard Giegé.

12 recordsLinked to original sources
PubMed2003

Yeast aspartyl-tRNA synthetase binds specifically its own mRNA.

Dimeric class II aspartyl-tRNA synthetase (AspRS) from yeast has a modular architecture and includes an N-terminal appendix of 70 amino acid residues that protrudes from the anticodon-binding module. This extension, of predicted helical structure, is not essential for aminoacylation but contains an RNA-binding motif that promotes non-specific interactions with tRNAs. As shown here, this protein extension can also interact with the 5' end of the AspRS mRNA. In vitro, optimal binding occurs on an mRNA domain comprising part of the 87 nucleotide long 5'UTR and the sequence encoding the N-terminal appendix. At the protein side, only the appendix and the anticodon-binding module participate in the interaction between AspRS and the mRNA domain. Binding is specific, since only tRNA(Asp) can dissociate the complex. In vivo, AspRS also binds specifically this mRNA domain and in doing so triggers a reduced translation of a fused GFP mRNA. From that, a mechanism for the regulation of this eukaryotic aminoacyl-tRNA synthetase is proposed. Implications for aspartylation accuracy in yeast are given.

5' Untranslated Regions↗
PubMed2003

Non-discriminating and discriminating aspartyl-tRNA synthetases differ in the anticodon-binding domain.

In most organisms, tRNA aminoacylation is ensured by 20 aminoacyl-tRNA synthetases (aaRSs). In eubacteria, however, synthetases can be duplicated as in Thermus thermophilus, which contains two distinct AspRSs. While AspRS-1 is specific, AspRS-2 is non-discriminating and aspartylates tRNA(Asp) and tRNA(Asn). The structure at 2.3 A resolution of AspRS-2, the first of a non-discriminating synthetase, was solved. It differs from that of AspRS-1 but has resemblance to that of discriminating and archaeal AspRS from Pyrococcus kodakaraensis. The protein presents non-conventional features in its OB-fold anticodon-binding domain, namely the absence of a helix inserted between two beta-strands of this fold and a peculiar L1 loop differing from the large loops known to interact with tRNA(Asp) identity determinant C36 in conventional AspRSs. In AspRS-2, this loop is small and structurally homologous to that in AsnRSs, including conservation of a proline. In discriminating Pyrococcus AspRS, the L1 loop, although small, lacks this proline and is not superimposable with that of AspRS-2 or AsnRS. Its particular status is demonstrated by a loop-exchange experiment that renders the Pyrococcus AspRS non-discriminating.

Amino Acid Sequence↗
PubMed2003

Pathology-related substitutions in human mitochondrial tRNA(Ile) reduce precursor 3' end processing efficiency in vitro.

The human mitochondrial genome encodes 22 tRNAs interspersed among the two rRNAs and 11 mRNAs, often without spacers, suggesting that tRNAs must be efficiently excised. Numerous maternally transmitted diseases and syndromes arise from mutations in mitochondrial tRNAs, likely due to defect(s) in tRNA metabolism. We have systematically explored the effect of pathogenic mutations on tRNA(Ile) precursor 3' end maturation in vitro by 3'-tRNase. Strikingly, four pathogenic tRNA(Ile) mutations reduce 3'-tRNase processing efficiency (V(max) / K(M)) to approximately 10-fold below that of wild-type, principally due to lower V(max). The structural impact of mutations was sought by secondary structure probing and wild-type tRNA(Ile) precursor was found to fold into a canonical cloverleaf. Among the mutant tRNA(Ile) precursors with the greatest 3' end processing deficiencies, only G4309A displays a secondary structure substantially different from wild-type, with changes in the T domain proximal to the substitution. Reduced efficiency of tRNA(Ile) precursor 3' end processing, in one case associated with structural perturbations, could thus contribute to human mitochondrial diseases caused by mutant tRNAs.

Base Sequence↗
PubMed2002

Physical aspects of protein crystal growth investigated with the Advanced Protein Crystallization Facility in reduced-gravity environments.

The physicochemical aspects of protein crystallization in reduced-gravity environments ( micro g) have been investigated with the Advanced Protein Crystallization Facility during six space missions. This review summarizes the results, dealing with the mechanisms of nucleation and crystal growth and with the quality of the crystals that were obtained under reduced gravity as well as under normal gravity on earth. Statistical analyses of the experimental data strongly support the fact that micro g has a positive effect on crystallization and on crystal quality. A comparison of experiments and theories of protein crystallization in reduced-gravity environments is presented. Recommendations for improving the performance of protein crystallization experiments in micro g and on earth are discussed.

Animals↗
PubMed2002

Yeast tRNA(Asp) charging accuracy is threatened by the N-terminal extension of aspartyl-tRNA synthetase.

This study evaluates the role of the N-terminal extension from yeast aspartyl-tRNA synthetase in tRNA aspartylation. The presence of an RNA-binding motif in this extension, conserved in eukaryotic class IIb aminoacyl-tRNA synthetases, provides nonspecific tRNA binding properties to this enzyme. Here, it is assumed that the additional contacts the 70 amino acid-long appendix of aspartyl-tRNA synthetase makes with tRNA could be important in expression of aspartate identity in yeast. Using in vitro transcripts mutated at identity positions, it is demonstrated that the extension grants better aminoacylation efficiency but reduced specificity to the synthetase, increasing considerably the risk of noncognate tRNA mischarging. Yeast tRNA(Glu(UUC)) and tRNA(Asn(GUU)) were identified as the most easily mischarged tRNA species. Both have a G at the discriminator position, and their anticodon differs only by one change from the GUC aspartate anticodon.

Amino Acid Motifs↗
PubMed2002

Crystallization in the presence of glycerol displaces water molecules in the structure of thaumatin.

The intensely sweet protein thaumatin has been crystallized at 293 K in the presence of sodium tartrate and 25%(v/v) glycerol for X-ray diffraction data collection at 100 K. A comparison of the three-dimensional structure model derived from a crystal grown in the presence of glycerol with that of a control deprived of this additive reveals only minor changes in the overall structure but a approximately 20% reduction in the number of water molecules. X-ray topography analyses show that the overall quality of the crystals prepared in the presence of this cryoprotectant is enhanced.

Crystallization↗
PubMed2002

Crystal contacts engineering of aspartyl-tRNA synthetase from Thermus thermophilus: effects on crystallizability.

To understand how surface residues in a protein structure influence crystal growth, packing arrangement and crystal quality, crystal surfaces were modified and crystallizability of seven different mutants investigated. The model was aspartyl-tRNA synthetase-1 from Thermus thermophilus, a homodimer (M(r) 122000) with a subunit of 580 amino acids. Engineering concerned modification of amino acids involved in packing contacts in the orthorhombic lattice (P2(1)2121) of the synthetase. Comparison of the crystallization behaviour of the mutants indicates a correlation between disruption/addition of packing interactions and crystallizability of the mutants: disruption or modification of lattice contacts prevents crystallization or leads to crystals of poor quality. In contrast, addition of potential contacts leads to well-shaped crystals of same space group and cell parameters than wild-type crystals.

Aspartate-tRNA Ligase↗
PubMed2002

Towards atomic resolution with crystals grown in gel: the case of thaumatin seen at room temperature.

One reason for introducing a gel in the crystallization medium of proteins is its ability to reduce convection in solution. This can lead to better nucleation and growth conditions, and to crystals having enhanced diffraction properties. We report here the X-ray characterization at room temperature of high-quality crystals of the intensely sweet thaumatin prepared in a sodium tartrate solution gelified with 0.15% (m/v) agarose. Using a synchrotron radiation, these crystals diffracted to a previously unachieved resolution. A diffraction dataset was collected from four crystals at a resolution of 1.2 A with a R(sym) of 3.6% and a completeness of 99%. Refinement was carried out to a final crystallographic R-factor of 12.0%. The quality of the electron density map allowed for the observation of fine structural details in the protein and its solvation shell. Crystallization in gel might be used more generally to improve the quality of macromolecular crystals. Advantages provided by the gelified medium in the frame of structural studies are emphasized.

Crystallization↗
PubMed2002

Comparative analysis of space-grown and earth-grown crystals of an aminoacyl-tRNA synthetase: space-grown crystals are more useful for structural determination.

Protein crystallization under microgravity aims at benefiting from the quasi-absence of convection and sedimentation to favor well ordered crystal nucleation and growth. The dimeric multidomain enzyme aspartyl-tRNA synthetase from Thermus thermophilus has been crystallized within dialysis reactors of the Advanced Protein Crystallization Facility in the laboratory on earth and under microgravity aboard the US Space Shuttle. A strictly comparative crystallographic analysis reveals that the crystals grown in space are superior in every respect to control crystals prepared in otherwise identical conditions on earth. They diffract X-rays more intensely and have a lower mosaicity, facilitating the process of protein structure determination. Indeed, the electron-density map calculated from diffraction data of space-grown crystals contains considerably more detail. The resulting three-dimensional structure model at 2.0 A resolution is more accurate than that produced in parallel using the data originating from earth-grown crystals. The major differences between the structures, including the better defined amino-acid side chains and the higher order of bound water molecules, are emphasized.

Amino Acyl-tRNA Synthetases↗
PubMed2002

Binding of tobramycin leads to conformational changes in yeast tRNA(Asp) and inhibition of aminoacylation.

Aminoglycosides inhibit translation in bacteria by binding to the A site in the ribosome. Here, it is shown that, in yeast, aminoglycosides can also interfere with other processes of translation in vitro. Steady-state aminoacylation kinetics of unmodified yeast tRNA(Asp) transcript indicate that the complex between tRNA(Asp) and tobramycin is a competitive inhibitor of the aspartylation reaction with an inhibition constant (K(I)) of 36 nM. Addition of an excess of heterologous tRNAs did not reverse the charging of tRNA(Asp), indicating a specific inhibition of the aspartylation reaction. Although magnesium ions compete with the inhibitory effect, the formation of the aspartate adenylate in the ATP-PP(i) exchange reaction by aspartyl-tRNA synthetase in the absence of the tRNA is not inhibited. Ultraviolet absorbance melting experiments indicate that tobramycin interacts with and destabilizes the native L-shaped tertiary structure of tRNA(Asp). Fluorescence anisotropy using fluorescein-labelled tobramycin reveals a stoichiometry of one molecule bound to tRNA(Asp) with a K(D) of 267 nM. The results indicate that aminoglycosides are biologically effective when their binding induces a shift in a conformational equilibrium of the RNA.

Acylation↗
PubMed2002

Comparative proteomics as a new tool for exploring human mitochondrial tRNA disorders.

More than 70 different point mutations in human mitochondrial tRNA genes are correlated with severe disorders, including fatal cardiopathies, encephalopathies, myopathies, and others. So far, investigation of the molecular impact(s) of mutations has focused on the affected tRNA itself by seeking structural and/or functional perturbations capable of interfering with synthesis of the 13 mitochondrion-encoded subunits of respiratory chain complexes. Here, a proteomic approach was used to investigate whether such mutations would affect the pattern of mitochondrial proteins at a broader level. Analysis of several hundred mitochondrial proteins from sibling cybrid cell lines by two-dimensional electrophoresis, an approach that takes into account all regulatory steps of mitochondrial and nuclear gene expression, indeed reveals a number of up- and downregulated proteins when healthy and single-point-mutation-carrying mitochondria representative of either MELAS or MERRF syndrome were compared. Assignment by mass spectrometry of the two proteins which exhibit obvious large quantitative decreases in the levels of both pathologic mitochondria identified nuclear-encoded subunits of cytochrome c oxidase, a respiratory chain complex. This clearly shows a linkage between the effects of mutations in mitochondrial tRNA genes and the steady-state level of nuclear-encoded proteins in mitochondria. It opens new routes toward a large-scale exploration of potential proteic partners involved in the genotype-phenotype correlation of mitochondrial disorders.

Amino Acid Sequence↗