The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform
Dieter Söll - One of the best experts on this subject based on the ideXlab platform.
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Anticodon and acceptor stem nucleotides in tRNAGln are major recognition elements for E. coli glutaminyl-tRNA synthetase
Nature, 1991Co-Authors: Martina Jahn, Dieter SöllAbstract:The correct attachment of amino acids to their corresponding (cognate) transfer RNA catalysed by aminoacyl-tRNA synthetases is a key factor in ensuring the fidelity of protein biosynthesis. Previous studies have demonstrated that the interaction of Escherichia coli tRNA(Gln) with glutaminyl-tRNA synthetase (GlnRS) provides an excellent system to study this highly specific recognition process, also referred to as 'tRNA identity'. Accurate acylation of tRNA depends mainly on two principles: a set of nucleotides in the tRNA molecule (identity elements) responsible for proper discrimination by aminoacyl-tRNA synthetases and competition between different synthetases for tRNAs. Elements of glutamine identity are located in the anticodon and in the acceptor stem region, including the discriminator base. We report here the production of more than 20 tRNA(2Gln) mutants at positions likely to be involved in tRNA discrimination by the enzyme. Unmodified tRNA, containing the wild-type anticodon and U or G at its 5'-terminus, can be aminocylated by GlnRS with similar kinetic parameters to native tRNA(2Gln). By in vitro aminoacylation the mutant tRNAs showed decreases of up to 3 x 10(5)-fold in the Specificity Constant (kcat/KM)14 with the major contribution of kcat. Despite these large changes, some of these mutant tRNAs are efficient amber suppressors in vivo. Our results show that strong elements for glutamine identity reside in the anticodon region and in positions 2 and 3 of the acceptor stem, and that the contribution of different identity elements to the overall discrimination varies significantly. We discuss our data in the light of the crystal structure of the GlnRS:tRNA(Gln) complex.
Martina Jahn - One of the best experts on this subject based on the ideXlab platform.
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Anticodon and acceptor stem nucleotides in tRNAGln are major recognition elements for E. coli glutaminyl-tRNA synthetase
Nature, 1991Co-Authors: Martina Jahn, Dieter SöllAbstract:The correct attachment of amino acids to their corresponding (cognate) transfer RNA catalysed by aminoacyl-tRNA synthetases is a key factor in ensuring the fidelity of protein biosynthesis. Previous studies have demonstrated that the interaction of Escherichia coli tRNA(Gln) with glutaminyl-tRNA synthetase (GlnRS) provides an excellent system to study this highly specific recognition process, also referred to as 'tRNA identity'. Accurate acylation of tRNA depends mainly on two principles: a set of nucleotides in the tRNA molecule (identity elements) responsible for proper discrimination by aminoacyl-tRNA synthetases and competition between different synthetases for tRNAs. Elements of glutamine identity are located in the anticodon and in the acceptor stem region, including the discriminator base. We report here the production of more than 20 tRNA(2Gln) mutants at positions likely to be involved in tRNA discrimination by the enzyme. Unmodified tRNA, containing the wild-type anticodon and U or G at its 5'-terminus, can be aminocylated by GlnRS with similar kinetic parameters to native tRNA(2Gln). By in vitro aminoacylation the mutant tRNAs showed decreases of up to 3 x 10(5)-fold in the Specificity Constant (kcat/KM)14 with the major contribution of kcat. Despite these large changes, some of these mutant tRNAs are efficient amber suppressors in vivo. Our results show that strong elements for glutamine identity reside in the anticodon region and in positions 2 and 3 of the acceptor stem, and that the contribution of different identity elements to the overall discrimination varies significantly. We discuss our data in the light of the crystal structure of the GlnRS:tRNA(Gln) complex.
Marius Brazaitis - One of the best experts on this subject based on the ideXlab platform.
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“Two sides of the same coin”: Constant motor learning speeds up, whereas variable motor learning stabilizes, speed–accuracy movements
European Journal of Applied Physiology, 2020Co-Authors: Albertas Skurvydas, Andrius Satas, Dovile Valanciene, Gediminas Mamkus, Dalia Mickeviciene, Daiva Majauskiene, Marius BrazaitisAbstract:Purpose The aim of this study was to determine the time course of the trade-off between speed and accuracy, intraindividual variability, and movement transfer and retention (4 weeks after learning) of speed–accuracy tasks. Methods The participants in this study were healthy adults randomly divided into three groups (control versus Constant versus variable). They were aged 19–24 years, and 30 (15 men and 15 women) were in each group. Participants had to perform various tasks with the right dominant hand: (a) simple reaction test; (b) maximal velocity measurement; and (c) a speed–accuracy task. Results During Constant and variable learning, the trade-off in a speed–accuracy task in specific situations shifted toward improved motor planning and motor execution speed, and to reduced intraindividual variability. However, during variable learning, the maximal velocity and variability of motor planning time did not change. Constant learning effectively transferred into variable tasks in terms of reaction time, average velocity and maximal velocity, and these effects were greater than those associated with variable learning. However, the effects of Constant learning did not transfer fully into the performance variability of variable movements. Variable learning effectively transferred into Constant tasks for the coefficient of variation of the path of movement, average velocity, maximal velocity and reaction time. The retention effect depended neither on learning nor task Specificity (Constant versus variable tasks). Conclusion Constant learning speeds up but does not stabilize speed–accuracy movements in variable tasks; whereas, variable learning stabilizes but does not speed up speed–accuracy movements in Constant tasks.
Garabed Antranikian - One of the best experts on this subject based on the ideXlab platform.
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purification and properties of a highly thermostable sodium dodecyl sulfate resistant and stereospecific proteinase from the extremely thermophilic archaeon thermococcus stetteri
Applied and Environmental Microbiology, 1995Co-Authors: M Klingeberg, B Galunsky, Volker Kasche, Carina Sjöholm, Garabed AntranikianAbstract:The cultivation of the extremely thermophilic archaeon Thermococcus stetteri in a dialysis membrane reactor was paralleled by the production of an extremely heat-stable proteinase(s). By applying preparative sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, an SDS-resistant proteinase was purified 67-fold in one step with a yield of 34%. The purified enzyme, which was composed of a single polypeptide chain with a molecular mass of 68 kDa, showed a broad temperature and pH profile (50 to 100(deg)C; pH 5 to 11). The optimal activity with substantial thermal stability was measured with casein at 85(deg)C and pH 8.5 to 9. Inhibition by phenylmethylsulfonyl fluoride and diisopropylfluorophosphate demonstrated that the enzyme was a serine proteinase. The enzyme displayed a relatively narrow substrate Specificity, catalyzing the hydrolysis only of N-protected p-nitroanilides or p-nitrophenyl esters of basic (Arg or Lys) or hydrophobic (Phe or Tyr) l-amino acids. l-Phenylglycine amide was also attacked by the proteinase, but with a lower Specificity Constant. Within the detection limit, no hydrolysis of d-amino acid derivatives was observed. The catalytic efficiency of the enzyme at 80(deg)C (k(infcat)/K(infm) for benzoyl-Arg-p-nitroanilide, 10(sup4)) is the same order of magnitude when compared with that of functionally similar mesophilic enzymes. The proteinase also acts as a transferase, catalyzing the acyl transfer from protected amino acid ester or amide to amino acid amide. The observed thermostability, SDS resistance, relatively narrow substrate Specificity, high stereoSpecificity, and limited catalytic efficiency probably reflect the tighter packing of the thermostable protein molecule and its limited flexibility. This was supported by fluorescence spectra of the enzyme, mainly due to tryptophan residues, in the temperature range of 30 to 90(deg)C. Structural reorganization was observed at temperatures over 100(deg)C. The results obtained could be of relevance for the better understanding of the structure-function relationship of enzymes from extreme thermophiles and suggest possible biotechnological application of the proteinase for resolution of racemic mixtures.
Michael F Dunn - One of the best experts on this subject based on the ideXlab platform.
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Biochemical characterization of a Rhizobium etli monovalent cation-stimulated acyl-coenzyme A carboxylase with a high substrate Specificity Constant for propionyl-coenzyme A.
Microbiology (Reading England), 2020Co-Authors: Michael F Dunn, Gisela Araiza, Jaime MoraAbstract:Biotin has a profound effect on the metabolism of rhizobia. It is reported here that the activities of the biotin-dependent enzymes acetyl-coenzyme A carboxylase (ACC; EC 6.4.1.2) and propionyl-coenzyme A carboxylase (PCC; EC 6.4.1.3) are present in all species of the five genera comprising the Rhizobiaceae which were examined. Evidence is presented that the ACC and PCC activities detectable in Rhizobium etli extracts are catalysed by a single acyl-coenzyme A carboxylase. The enzyme from R. etli strain 12-53 was purified 478-fold and displayed its highest activity with propionyl-CoA as substrate, with apparent K(m) and V(max) values of 0.064 mM and 2885 nmol min(-1) (mg protein)(-1), respectively. The enzyme carboxylated acetyl-CoA and butyryl-CoA with apparent K(m) values of 0.392 and 0.144 mM, respectively, and V(max) values of 423 and 268 nmol min(-1) (mg protein)(-1), respectively. K(+), or Cs(+) markedly activated the enzyme, which was essentially inactive in their absence. Electrophoretic analysis indicated that the acyl-CoA carboxylase was composed of a 74 kDa biotin-containing alpha subunit and a 45 kDa biotin-free beta subunit, and gel chromatography indicated a total molecular mass of 620 000 Da. The strong kinetic preference of the enzyme for propionyl-CoA is consistent with its participation in an anaplerotic pathway utilizing this substrate.
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biochemical characterization of a rhizobium etli monovalent cation stimulated acyl coenzyme a carboxylase with a high substrate Specificity Constant for propionyl coenzyme a
Microbiology, 2004Co-Authors: Michael F Dunn, Gisela Araiza, Jaime Font De MoraAbstract:Biotin has a profound effect on the metabolism of rhizobia. It is reported here that the activities of the biotin-dependent enzymes acetyl-coenzyme A carboxylase (ACC; EC 6.4.1.2) and propionyl-coenzyme A carboxylase (PCC; EC 6.4.1.3) are present in all species of the five genera comprising the Rhizobiaceae which were examined. Evidence is presented that the ACC and PCC activities detectable in Rhizobium etli extracts are catalysed by a single acyl-coenzyme A carboxylase. The enzyme from R. etli strain 12-53 was purified 478-fold and displayed its highest activity with propionyl-CoA as substrate, with apparent K m and V max values of 0·064 mM and 2885 nmol min−1 (mg protein)−1, respectively. The enzyme carboxylated acetyl-CoA and butyryl-CoA with apparent K m values of 0·392 and 0·144 mM, respectively, and V max values of 423 and 268 nmol min−1 (mg protein)−1, respectively. K+, or Cs+ markedly activated the enzyme, which was essentially inactive in their absence. Electrophoretic analysis indicated that the acyl-CoA carboxylase was composed of a 74 kDa biotin-containing α subunit and a 45 kDa biotin-free β subunit, and gel chromatography indicated a total molecular mass of 620 000 Da. The strong kinetic preference of the enzyme for propionyl-CoA is consistent with its participation in an anaplerotic pathway utilizing this substrate.