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G Winter

Publications and source records attributed to G Winter.

At least 163 records · Page 9Linked to original sources
PubMed1987

Structure-activity relationships in engineered proteins: characterization of disruptive deletions in the alpha-ammonium group binding site of tyrosyl-tRNA synthetase.

Residues Asp-78 and Gln-173 of the tyrosyl-tRNA synthetase of Bacillus stearothermophilus form part of the binding site for tyrosine by making hydrogen bonds with the alpha-ammonium group. Asp-38 is close enough to the group to make an important electrostatic contribution. Unlike other residues in the active site that have been studied by site-directed mutagenesis, Asp-38, Asp-78, and Gln-173 are part of hydrogen-bonded networks. Each of these residues has been mutated to an alanine, and the resultant mutants have been studied by kinetics to construct the difference energy diagrams for the formation of tyrosyl adenylate. In each example, the binding of tyrosine is weakened by about 2.5 kcal mol-1. But, unlike previous mutants, the dissociation of the second substrate, in this case ATP, is also seriously affected, being weakened by some 2 kcal mol-1 for TyrTS(Ala-78) and TyrTS(Ala-173). The energy of the transition state for the formation of tyrosyl adenylate is raised by 7.8 kcal mol-1 for the former and 4.5 kcal mol-1 for the latter mutant. Addition of these mutants to linear free energy plots constructed for the nondisruptive mutants in the accompanying study [Fersht, A. R., Leatherbarrow, R. J., & Wells, T. N. C. (1987) Biochemistry (preceding paper in this issue)] reveals large deviations of the data for TyrTS(Ala-38) and TyrTS(Ala-78) from the regression line. These thus belong to a different class of mutations from previous nondisruptive examples. This observation combined with the structural evidence and difference energy diagrams strongly suggests that the mutations Asp----Ala-38 and Asp----Ala-78 are disruptive in nature.

Amino Acyl-tRNA Synthetases↗
PubMed1986

A transcription terminator in the 5' non-coding region of the tyrosyl tRNA synthetase gene from Bacillus stearothermophilus.

The 5' non-coding region of the tyrosyl-tRNA synthetase gene (tyrS) of Bacillus stearothermophilus is 324 nucleotides long. It contains a premature terminator and a strong promoter: these were identified in vitro by RNA run-off experiments and in Escherichia coli by construction of specific mutants. The terminator consists of a stem and loop structure followed by the string of T residues characteristic of rho-independent termination. This is preceded by another stem and loop structure which may permit the formation of an anti-terminator. Neither the promoter nor the premature terminator appears to be regulated by the tyrosyl-tRNA synthetase in vitro or in E. coli.

Amino Acyl-tRNA Synthetases↗
PubMed1986

Kinetics of allergen release from house dust mite Dermatophagoides pteronyssinus.

Purified bodies of Dermatophagoides pteronyssinus were extracted over different extraction times. The release kinetics of proteins, carbohydrates, and allergens were assessed by different methods. Additional attempts have been made to elucidate the extraction process also on a molecular basis. For this purpose the extracts were analyzed by isoelectric focusing, SDS gel electrophoresis, crossed radioimmunoelectrophoresis, and an immunoprint technique. Carbohydrates, proteins, and allergens were released immediately from the mite bodies but demonstrated different release kinetics. The release of carbohydrates and proteins was linear up to 48 hours but demonstrated different slopes. The major allergen P1 demonstrated steady release up to 48 hours, whereas the overall allergenic activity as determined by RAST inhibition demonstrated typical saturation kinetics reaching a plateau after 4 to 5 hours of extraction. It was demonstrated by parallel-line assay of the RAST-inhibition curves that the allergenic determinants remained unchanged up to 48 hours. Different electrophoretic methods demonstrated that all relevant proteins and allergens were released immediately from the mite bodies. The electrophoretic patterns changed only slightly up to 4 hours. Prolonged extraction times up to 48 hours did not affect the patterns. This makes a loss of proteins or allergens by degradation unlikely.

Allergens↗
PubMed1986

Construction of heterodimer tyrosyl-tRNA synthetase shows tRNATyr interacts with both subunits.

The tyrosyl-tRNA synthetase (EC 6.1.1.1) from Bacillus stearothermophilus is a dimer of two identical subunits. The dimer shows "half-of-the-sites" reactivity in that only one molecule of tyrosyladenylate is formed and one molecule of tRNATyr binds per dimer. To identify whether the tRNATyr binds to a single subunit in the dimer, or to both subunits, heterodimers were constructed by mixing two variant dimers together in 8 M urea. As the unfolded protein is electrophoresed into a native polyacrylamide gel, it refolds and reassociates, and heterodimers can be purified from the parental dimers. Kinetic analysis of heterodimers formed between variant enzymes with defective tyrosine activation or tRNA aminoacylation shows that a molecule of tRNATyr interacts with the N-terminal region of one subunit and the C-terminal region of the other subunit in the dimer.

Amino Acyl-tRNA Synthetases↗
PubMed1986

Reduced heat resistance of mutant spores after cloning and mutagenesis of the Bacillus subtilis gene encoding penicillin-binding protein 5.

Part of the gene encoding penicillin-binding protein 5 from Bacillus subtilis 168 was cloned in Escherichia coli with a synthetic oligonucleotide as a hybridization probe. The gene was designated dacA by analogy with E. coli. The nucleotide sequence was determined, and the predicted molecular mass was 45,594 daltons (412 amino acids). A comparison of the predicted amino acid sequence with that of the E. coli penicillin-binding protein 5 indicated that these enzymes showed about 25% identity. The B. subtilis dacA gene was mutated by integration of a plasmid into the structural gene by homologous recombination. A comparison of the mutant and control strains revealed that (i) the mutant lacked detectable penicillin-binding protein 5, (ii) the D-alanine carboxypeptidase activity of membranes isolated from the mutant was only 5% of that measured in membranes from the control strain, (iii) the mutant cells showed apparently normal morphology only during exponential growth, and after the end of exponential phase the cells became progressively shorter, (iv) the mutant sporulated normally except that the forespore occupied about two-thirds of the mother cell cytoplasm and, during its development, migrated towards the center of the mother cell, and (v) purified mutant spores were 10-fold less heat resistant but possessed normal refractility and morphology. Preliminary chemical analysis indicated that the structure of the cortex of the mutant was different.

Amino Acid Sequence↗
PubMed1985

EcoK selection vectors for shotgun cloning into M13 and deletion mutagenesis.

For shotgun cloning into M13 vectors, a double-stranded cassette of synthetic oligonucleotides containing a SmaI site within the two halves of an EcoK site, has been introduced into the vector M13mp8. Cloning of blunt end DNA into the SmaI site destroys the EcoK site, and recombinants are therefore preferentially selected on transfection into a K strain of E.coli. For deletion mutagenesis using synthetic oligonucleotides, an M13 vector with four copies of the EcoK cassette has been made to facilitate the joining of lacZ or a Factor Xa cleavage site to any protein reading frame.

Base Sequence↗
PubMed1985

Reversible dissociation of dimeric tyrosyl-tRNA synthetase by mutagenesis at the subunit interface.

Dimeric tyrosyl-tRNA synthetase from Bacillus stearothermophilus exhibits half-of-the-sites reactivity and negative cooperativity in binding of tyrosine. Protein engineering has been applied to the enzyme to determine whether it can be reversibly dissociated into monomers and if the monomers are active. The target for mutation is the residue Phe-164. The side chain of Phe-164 in one subunit interacts with its symmetry-related partner in the other. Mutation of Phe-164----Asp-164 gives a mutant [TyrTS(Asp-164)] that undergoes dissociation at high pH when the aspartate residues are ionized. The monomer is inactive and does not bind tyrosine. Dissociation is enhanced at low concentrations of enzyme by a mass action effect. Kinetic and binding measurements on TyrTS(Asp-164) with tyrosine and tyrosyl adenylate show that the monomer has very weak affinity for these ligands. Accordingly, dimerization is favored by high concentrations of tyrosine and ATP since the dimeric form has a high affinity for the ligands. The presence of tRNA does not encourage dimer formation, and so it must bind to the monomer. TyrTS(Asp-164) is fully active at pH 6 where dimerization is favored but has low activity at pH 7.8 where dissociation is favored. It should now prove possible to engineer heterodimers that may be used to investigate the subunit interactions further.

Amino Acyl-tRNA Synthetases↗
PubMed1985

Fine structure-activity analysis of mutations at position 51 of tyrosyl-tRNA synthetase.

Residue Thr-51 at the active site of tyrosyl-tRNA synthetase (Bacillus stearothermophilus) has been replaced with all the smaller amino acids by protein engineering to investigate direct and indirect effects of mutation on substrate binding and catalysis. The gamma-hydroxyl group of Thr-51 was thought to be 0.5 A too far from the ribose ring oxygen of ATP to form a hydrogen bond. Consistent with this, it is found that mutation of Thr-51----Cys-51, which should place the gamma-thiol group within its correct distance for hydrogen bonding, increases the affinity of the enzyme for ATP. Other mutations (Ser-51, Ala-51, and Gly-51) show the contributions to binding of the other atoms in the side chain of Thr-51. A family of enzymes has been produced, TyrTS(Thr-51) (wild type), TyrTS(Ala-51), TyrTS(Cys-51), and TyrTS(Pro-51), in which the value of kcat/KM for ATP in aminoacylation increases along the series. This is achieved by the value of KM decreasing significantly (2.5, 1.25, 0.29, and 0.019 mM, respectively) while there are smaller decreases in kcat (4.7, 4.0, 2.9, and 1.8 s-1, respectively). These variations cause each one of the enzymes to be more active than the others at particular concentrations of ATP. For example, at concentrations of ATP greater than 5.9 mM, TyrTS(Thr-51) is the most active, while TyrTS(Ala-51), TyrTS(Cys-51), and TyrTS(Pro-51) are the most active at 5.9-2.2, 2.2-0.42, and less than 0.42 mM ATP, respectively. Interestingly, position 51 shows variation in tyrosyl-tRNA synthetases isolated from different organisms.

Adenosine Triphosphate↗
PubMed1985

Probing histidine-substrate interactions in tyrosyl-tRNA synthetase using asparagine and glutamine replacements.

We have analyzed the interactions of a histidine residue with a substrate using site-directed mutagenesis. Previous studies on tyrosyl-tRNA synthetase from Bacillus stearothermophilus have shown that a histidine residue (His-48) makes an interaction with ATP, which is improved on mutating Thr-51----Pro-51. We find on replacing His-48 in wild-type enzyme with either asparagine or glutamine that Asn-48 is equally as good as His-48 but His-48----Gln-48 leads to a far lower activity. The side chain of an asparagine residue may be superimposed on that of a histidine so that the amide-NH2 group of asparagine occupies the same position as the pi-N of histidine, whereas the equivalent -NH2 group of glutamine may be superimposed upon the tau-N. This suggests that it is the pi-N of histidine that hydrogen bonds with ATP and that there is no significant electrostatic interaction between the histidine and ATP. Incorporating the Pro-51 mutation into each of the Asn-48 and Gln-48 mutants gives an improvement in the affinity of the enzyme for ATP, but this improvement is less than that seen with the wild-type enzyme.

Amino Acid Sequence↗
PubMed1985

Improved oligonucleotide site-directed mutagenesis using M13 vectors.

An improved method is described for the construction of mutations in M13 vectors using synthetic oligonucleotides. The DNA is first cloned into a novel M13 vector (based upon M13mp18 or M13mp19), which carries a genetic marker that can be selected against, such as an EcoK or EcoB site, or an amber mutation in an essential phage gene. In this "coupled priming" technique, one primer is used to construct the silent mutation of interest, and a second primer is used to eliminate the selectable marker on the minus strand. After primer extension and ligation, the heteroduplex DNA is transfected into a strain of E. coli which is repair deficient and selects against the plus strand marker. Over 50 mutants have been constructed with this approach, and the yields can be excellent (up to 70%). For the stepwise construction of mutations using separate rounds of mutagenesis, the EcoK and EcoB markers offer a particular advantage over the amber marker. They permit selection in each round, as it is possible to cycle between the two markers. However for construction of multiple mutations over a short region, long synthetic oligonucleotides with multiple mismatches to the template can offer an alternative strategy.

Base Sequence↗
PubMed1985

Transition-state stabilization in the mechanism of tyrosyl-tRNA synthetase revealed by protein engineering.

The principal catalytic factor in the activation of tyrosine by the tyrosyl-tRNA synthetase is found to be improved binding of ATP in the transition state. The activation reaction involves the attack of the tyrosyl carboxylate on the alpha-phosphate group of ATP to generate a pentacoordinate transition state. Model building of this complex located a binding site for the gamma-phosphate group of ATP, consisting of hydrogen bonds with the side chains of Thr-40 and His-45. Removal of these groups by protein engineering shows that they contribute no binding energy with unreacted ATP but put all of their binding energy into stabilizing the [tyrosine-ATP] transition state [the mutant tyrosyl-tRNA synthetase (Thr-40----Ala-40; His-45----Gly-45) has the rate of formation of tyrosyl adenylate lowered by 3.2 X 10(5) but KS for ATP is lowered by only a factor of 5]. The side chains of these residues also provide a binding site for pyrophosphate in the reverse reaction. Thus, catalysis is accomplished by stabilization of the transition state by improved binding of a group on the substrate that is distant from the seat of reaction.

Adenosine Triphosphate↗
PubMed1985

[Malfunction of equipment by the addition of a bacterial filter in the expiratory branch of the respiratory circuit].

The addition of a continuous Flow System to the circuit of a volume cycled respirator results in an additional IMV option and shows excellent performance for this purpose. The insertion of a bacterial filter into this modified circuit resulted in a dangerous increase of airway pressures after 54 "running hours" for that filter. Test series revealed an insufficient air transmission through the filter, caused by the water vapour-saturated inspiratory gas mixture, which is necessary in long term ventilation. Furthermore it was demonstrated that wet bacterial filters cause malfunction of SIMV systems due to interference with the demand valve responsible for proper air supply. The routine use of a bacterial filter placed in the expiratory branch results in higher risks in an already risky artificial ventilation system and use-nonuse relationships seem to be questionable.

Adult↗
PubMed1984

Estrogen receptor status and adjuvant polychemotherapy or antiestrogen therapy in patients with high-risk breast cancer.

This pilot study includes 115 consecutive patients admitted in the period from 1978 to 1981. Patients eligible for this study were at high risk according to the TNM classification with stages pT1-pT3 and pN+, MO. Primary therapy included modified radical mastectomy and axillary-node clearance, one or more ipsilateral nodes being involved in routine histology. All tumors were assayed for estrogen and progesterone receptors. According to the result of the estrogen receptor assay, estrogen-receptor-positive patients were treated with Tamoxifen 30 mg/day for a period of 2 years. Estrogen-receptor-negative patients were treated with cytoxan, methotrexate, and 5-fluorouracil or adriblastin, cytoxan. After a median observation time of 36 months, overall there have been 31 recurrences: 9 = 17.3% in the estrogen-receptor-positive group and 22 = 34.9% in the estrogen-receptor-negative group. The analysis of different subgroups showed no significant differences, either in relation to axillary lymph-node status or in relation to menopausal status in the endocrine-treated compared with the polychemotherapy group. This result suggests, especially in the subgroup of patients with involvement of one to three axillary nodes, that estrogen-receptor-positive and estrogen-receptor-negative patients should be considered as separate groups when adjuvant therapy is indicated. Possibly hormone-receptor-positive patients may benefit from endocrine therapy and do not need polychemotherapy.

Adult↗
PubMed1984

The use of double mutants to detect structural changes in the active site of the tyrosyl-tRNA synthetase (Bacillus stearothermophilus).

In a previous study, a mutant of tyrosyl-tRNA synthetase in which a threonine residue (Thr51) was converted to proline dramatically improved the affinity of the enzyme for its ATP substrate. How does Pro51 improve the enzyme's affinity for ATP? A priori, Pro51 might interact directly with the ATP, or it might distort the polypeptide backbone and thereby force new or improved contacts elsewhere from the enzyme to ATP. By making mutants of the Pro51 enzyme at two residues that make hydrogen bonds to the ATP substrate, we show that Pro51 greatly improves the strength of one of these contacts. Thus the propagation of a structural change in an enzyme induced by mutation may be detected by the introduction of further mutations.

Amino Acyl-tRNA Synthetases↗
PubMed1984

Treatment of chronic active hepatitis--present state.

Nowadays, both Anglo-Saxon and Middle European pathologists define chronic active hepatitis as synonymous with chronic aggressive hepatitis (CAH) without cirrhotic transformation. For its treatment, an accurate determination of the histological stage is necessary. CAH with slight to moderate activity (type 2a) requires merely general treatment, while corticosteroids and/or immunosuppressives are contraindicated. The latter drugs are indicated only for HBs- and HBeAG-negative CAH of type 2b with marked inflammatory activity. Every case should, however, be carefully assessed to determine whether these drugs might not be contraindicated. Our own experience with more than 600 patients with CAH shows that the prognosis is most favourable in HBs- and HBeAg-negative patients, in whom pre-existing chronic infections have been quickly recognized and eradicated, and in whom corticosteroids and/or immunosuppressives were not required. In the meantime, 13% of the CAH patients without cirrhotic transformation have been cured, and 42.5% improved. In contrast, CAH treatment with interferon, Virazol, arabinoside and immunostimulation remain disappointing.

Biopsy, Needle↗