Isoleucyl‐tRNA synthetase from baker's yeast

Freist, Wolfgang; Sternbach, Hans

doi:10.1111/j.1432-1033.1989.tb14487.x

Cited by 10 publications

(13 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This may indicate that in these cases the amino-acid-binding site is also complete on complex formation with valyl-tRNA synthetase and the modified tRNA. Similar observations have been made with tRNA11e-C-C-3'dA, which shows, in acylation with valine, the same initial discrimination factor ZI as that obtained in acylation of tRNA1"-C-C-A(3'NH2); in aminoacylation with other acids, the factors I ' are as observed in acylation of tRNA"'-C-C-A [18]. The overall Gibbs free energy of initial discrimination of 2-aminoisobutyric acid shows a very similar value (11.85 kJ/mol; 2.83 kcal/mol) to that found for initial discrimination of valine by isoleucyl-tRNA synthetase (14.25 kJ/mol; 3.41 kcal/mol) [l, 21.…”

Section: Coni'ludiiig Rernarkssupporting

confidence: 82%

Valyl‐tRNA synthetase from yeast

Freist

Cramer

1990

European Journal of Biochemistry

Self Cite

View full text Add to dashboard Cite

For discrimination between valine and the 19 naturally occurring noncognate amino acids, as well as between valine and 2-amino-isobutyric acid by valyl-tRNA synthetase from baker's yeast, discrimination factors (D) have been determined from k,,, and K , values in aminoacylation of tRNAVal-C-C-A. The lowest values were found for Trp, Ser, Cys, Lys, Met and Thr (D = 90 -870), showing that valine is 90 -870 times more frequently attached to tRNA""'-C-C-A than the noncognate amino acids at the same amino acid concentrations. The other amino acids exhibit D values between 1100 and 6200. Generally, valyl-tRNA synthetase is considerably less specific than isoleucyl-tRNA synthetase, but this may be partly compensated in the cell by valine concentrations higher than those of noncognate acids.In aminoacylation of tRNAVa'-C-C-A(3'NH2) discrimination factors D , are in the range of 40-1260. From D 1 values and AMP formation stoichiometry, pretransfer proof-reading factors n1 were determined; post-transfer proof-reading factors n2 were determined from D values and AMP formation stoichiometry in acylation of tRNAVal-C-C-A. n, values (7 -168) show that pretransfer proof-reading is the main correction step, posttransfer proof-reading (IT, z 1 -7) is less effective and in some cases negligible.Initial discrimination factors were calculated from discrimination and proof-reading factors according to a two-step binding process. These factors, due to different Gibbs free energies of binding can be related to hydrophobic interaction forces, and a hypothetical 'stopper' model of the amino-acid-binding site is discussed.In our recent work on amino acid specificity of aminoacyltRNA synthetases we found that no general error rate can be given for the aminoacylation of tRNA in the following reaction [ 1 -41 :

show abstract

Section: Coni'ludiiig Rernarkssupporting

confidence: 82%

Valyl‐tRNA synthetase from yeast

Freist

Cramer

1990

European Journal of Biochemistry

Self Cite

View full text Add to dashboard Cite

show abstract

“…and various concentrations of the R3-RNA (2 to 20 nM). From the data obtained we estimated a dissociation constant Kd of about 0.2 /AM which compares well with quantitative estimates for the interaction of several synthetases with their cognate tRNAs (16,17).…”

Section: Resultssupporting

confidence: 65%

Binding of human glutaminyl-tRNA synthetase to a specific site of its mRNA

Schray

Knippers

1991

Nucl Acids Res

View full text Add to dashboard Cite

The human glutaminyl-tRNA synthetase is able to bind to its own mRNA. The enzyme contains two binding regions. One is located in the central section of the enzyme which includes its most hydrophilic portion with ten lysine residues in a block of 20 amino acids. This part of the enzyme binds unspecifically to all RNA sequences tested. A second binding region is located in that part of the enzyme which shows high degrees of sequence similarities with the bacterial and yeast glutaminyl-tRNA synthetases, and which is most likely responsible for the charging of tRNA with glutamine. This second RNA binding region specifically interacts with a site in the 3' noncoding region of the synthetase's mRNA. The binding site in the mRNA is characterized by an extended secondary structure that includes elements of the 'identity set' of nucleotides recognized by the enzyme when interacting with tRNA. We discuss possible physiological implications of the interaction between glutaminyl-tRNA synthetase and its mRNA.

show abstract

“…After the binding of tRNA, a slow conformational change occurs, and after it the pretransfer proofreading is performed, The conformational change functions as a barrier which prevents the proofread adenylate from returning to early steps. Fersht [12] has suggested this kind of model as one explanation for the rates of decomposition of correct and incorrect aminoacyl adenylates or aminoacyl-tRNA:s. According to Freist et al [15], the AMP production is also Fast in the presence of tRNA modifications which are not able to bind the amino acid, therefore it is apparent that this proofreading really occurs before the transfer reaction. In addition, some other aminoacyl-tRNA synthetases show a 'conformational activation' after the binding of tRNA [16], thus the same mechanism could also work in the isoleucyl-tRNA synthetase.…”

Section: Resultsmentioning

confidence: 99%

Effect of inorganic pyrophosphate on the pretransfer proofreading in the isoleucyl‐tRNA synthetase from Escherichia coli

Airas

1992

European Journal of Biochemistry

View full text Add to dashboard Cite

A total rate equation was used to calculate the discrimination of valine by the isoleucyl-tRNA synthetase from Escherichia coli. The PPi present in the cell makes the backward reaction or the pyrophosphorolysis of the E .possible. If the E . Ile-AMP has been corrected for wrong aminoacyl adenylation by the pretransfer proofreading, the pyrophosphorolysis rapidly equilibrates the corrected E . Ile-AMp with E . and thus spoils the effect of the proofreading. The loss of the corrected species is avoided if there is a barrier (perhaps conformational) formed by a slow reaction step between the noncorrected E . l'e-AMP and the corrected *E$&Mp. If such a slow conformational change exists, the increase in accuracy from the pretransfer proofreading would be benefitial, and, in addition, the PPi increases the accuracy by optimizing the initial discrimination of the wrong amino acid.The activation of amino acids by the aminoacyl-tRNA synthetases produces PP,, which is able to bind to the aminoacyl adenylate in the reversc reaction [I]. Both the activation and the pyrophosphorolysis are rapid reactions [2] which allow an equilibrium at this step in the presence of PPi. The PPi strongly shifts the equilibrium from the aminoacyl adenylate intermediates towards the start of the total reaction. PP, is decomposed by the inorganic pyrophosphatase present in all living cells. The pyrophosphatase, however, does not destroy all PP,, but a moderate concentration is maintained. The PP, concentration in Escherichia roli cells, thoroughly studied in this laboratory [3 -51, is about 0.5 mM and is not changed very much by varying the conditions.The amino acid specificity of the aminoacyl-tRNA synthetases has been described to be increased in four steps [6]. Two initial discrimination steps occur before the activation reaction, the pretransfer proofreading works at the aminoacyl adenylate step and the posttransfer proofreading at the aminoacyl-tRNA step (Eqn 1).The effect of PP, on the aminoacyl-tRNA synthetase reaction has already been considered in two earlier papers on this work [7, 81. The present work uses the kinetic equations derived in the preceding paper [9]. The roles of PP, in the initial discriminations and pretransfer proofreading were calculated. MATERIALS AND METHODS EquationsThe rate equations were derived as suggested by Cha [lo] and as described in detail in the preceding paper [9]. The reaction scheme was divided in separate rapid equilibrium segments. Since the amino acid specificity is to be examined, the binding reaction for the amino acid makes one boundary of the segments, and the different amino acids, isoleucine and valine, have their own segments (Eqn 2).

show abstract

Isoleucyl‐tRNA synthetase from baker's yeast

Cited by 10 publications

References 26 publications

Valyl‐tRNA synthetase from yeast

Valyl‐tRNA synthetase from yeast

Binding of human glutaminyl-tRNA synthetase to a specific site of its mRNA

Effect of inorganic pyrophosphate on the pretransfer proofreading in the isoleucyl‐tRNA synthetase from Escherichia coli

Contact Info

Product

Resources

About