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Biomedical subjects

W H Ward

Publications and source records attributed to W H Ward.

At least 37 records · Page 2Linked to original sources
PubMed1989

Lymphocyte subpopulations in sheep during the early stage of experimental infection with bovine leukaemia virus.

Sheep were experimentally infected with bovine leukaemia virus (BLV) by the inoculation of PBL from leukaemic sheep. Antibodies to viral structural proteins were detected at from 2 to 6 weeks after inoculation. At seroconversion, all sheep had a marked increase in the number of circulating lymphocytes, due essentially to an increase in the number of B cells. The number of circulating B cells then decreased but remained higher than pre-infection levels. A second increase in this population preceded the development of a B cell lymphoblastic leukaemia. Generalized lymphosarcoma was diagnosed at necropsy of all sheep. Variation between individual sheep in the time from infection to the development of tumours allowed two clearly delineated groups of nine sheep to be compared. A study of changes in the B cell and T cell populations during the first 16 weeks of infection suggested that the initial response to infection influences the subsequent rate of leukaemogenesis. At seroconversion the number of circulating B cells was significantly higher in group 1 (10.16 +/- 1.51 X 10(9)/l) than in group 2 (6.47 +/- 2.76 X 10(9)/l). Group 1 sheep became leukaemic at 20-50 weeks after infection, whereas group 2 sheep did not do so until 70-95 weeks after infection.

Animals↗
PubMed1988

Tyrosyl-tRNA synthetase acts as an asymmetric dimer in charging tRNA. A rationale for half-of-the-sites activity.

Tyrosyl-tRNA synthetase from Bacillus stearothermophilus is a classical example of an enzyme with half-of-the-sites activity. The enzyme crystallizes as a symmetrical dimer that is composed of identical subunits, each having a complete active site. In solution, however, tyrosyl-tRNA synthetase binds tightly, and activates rapidly, only 1 mol of Tyr/mol of dimer. It has recently been shown that the half-of-the-sites activity results from an inherent asymmetry of the enzyme. Only one subunit catalyzes formation of Tyr-AMP, and interchange of activity between subunits is not detectable over a long time scale. Paradoxically, however, the kinetics of tRNA charging are biphasic with respect to [Tyr], suggesting that both subunits of the dimer are catalytically active. This paradox has now been resolved by kinetic analysis of heterodimeric enzymes containing different mutations in each subunit. Biphasic kinetics with unchanged values of KM for Tyr are maintained when one of the two tRNA-binding domains is removed and also when the affinity of the "inactive" site for Try is reduced by 2-58-fold. The biphasic kinetics do not result from catalysis at both active sites, but instead appear to result from two molecules of Tyr binding sequentially to the same site. A second molecule of Tyr perhaps aids the dissociation of Tyr-tRNA by displacing the tyrosyl moiety from its binding site. A monomer of the enzyme is probably too small to allow both recognition and aminoacylation of a tRNA molecule. This could explain the requirement for the enzyme to function as an asymmetric dimer.

Adenosine Triphosphate↗
PubMed1988

Asymmetry of tyrosyl-tRNA synthetase in solution.

The tyrosyl-tRNA synthetase from Bacillus stearothermophilus crystallizes as a symmetrical dimer with each subunit having a complete active site. The enzyme-substrate complexes, however, are known to be asymmetrical in solution because the enzyme exhibits half-of-the-sites activity by binding tightly only 1 mol of tyrosine or 1 mol of tyrosyl adenylate per mole of dimer. Evidence is now presented that the unligated enzyme is also asymmetrical in solution. Symmetry was investigated by construction of heterodimers containing one full-length subunit and one truncated subunit, allowing the introduction of different mutations into each monomer. Each dimer is active at only one site, but the site used is randomly distributed between the subunits. Each heterodimer thus consists of two equal populations, one activating tyrosine at a full-length subunit and the other at the truncated subunit. No detectable interconversion is found between active and inactive sites over several minutes either in the absence of substrates or when the enzyme is turning over in the steady state. Kinetic evidence implies that wild-type enzyme is inherently asymmetrical even in the absence of substrate.

Amino Acyl-tRNA Synthetases↗
PubMed1987

Effects of engineering complementary charged residues into the hydrophobic subunit interface of tyrosyl-tRNA synthetase. Appendix: Kinetic analysis of dimeric enzymes that reversibly dissociate into inactive subunits.

Wild-type tyrosyl-tRNA synthetase (TyrTS) from Bacillus stearothermophilus is a symmetrical dimer. Four different heterodimeric enzymes have been produced by site-directed mutagenesis at the subunit interface so that the monomers are linked by a potential salt bridge in a hydrophobic environment. The two Phe-164 residues of wild-type TyrTS are on the axis of symmetry and interact in a hydrophobic region of the subunit interface. Mutation of Phe-164 to aspartate or glutamate in full-length TyrTS and to lysine or arginine in an active truncated enzyme (delta TyrTS) induces reversible dissociation of the enzyme into inactive monomers. Mixing mutants in equimolar amounts produces four different heterodimers: TyrTS(Asp-164)-delta TyrTS(Lys-164); TyrTS(Asp-164)-delta TyrTS(Arg-164); TyrTS(Glu-164)-delta TyrTS(Lys-164); TyrTS(Glu-164)-delta TyrTS(Arg-164). A general method is derived for analyzing the kinetics of dimeric enzymes that reversibly dissociate into inactive subunits. Application to mutants of TyrTS allows estimation of dissociation constants (Kd values) for the dimers. At pH 7.8, the heterodimers have Kd values of 6-14 microM, whereas for homodimers Kd = 120-4000 microM. These values decrease to about 30 microM for homodimers of TyrTS(Asp-164), TyrTS(Glu-164), and delta TyrTS(Lys-164) when the pH favors uncharged forms of the side chains at position 164. Each of the four salt bridges engineered into the hydrophobic subunit interface of TyrTS appears, therefore, to be weak. These engineered salt bridges may be compared with naturally occurring ones. In the latter, there are complementary interactions between the charges in the salt bridge with polar groups in the protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acyl-tRNA Synthetases↗
PubMed1986

Protein engineering of homodimeric tyrosyl-tRNA synthetase to produce active heterodimers.

Heterodimers of tyrosyl-tRNA synthetase from Bacillus stearothermophilus have been produced by mutagenesis at the subunit interface. Oppositely charged groups have been engineered into the subunits so that they can form a complementary pair. Wild-type tyrosyl-tRNA synthetase is a symmetrical dimer in which the side chains of the 2 Phe-164 residues interact at the subunit interface. Phe-164 was mutated to Asp in tyrosyl-tRNA synthetase and to Lys in a truncated enzyme (des-(321-419)tyrosyl-tRNA synthetase) which lacks the two tRNA-binding sites, but which can catalyze pyrophosphate exchange. The size difference allows subunit association to be studied by gel filtration chromatography. These changes induce reversible dissociation from active dimers into inactive monomers at pH values which favor ionization at position 164. A mixture of the two mutants near neutral pH is apparently fully active in pyrophosphate exchange and consists of a heterodimer of [Asp164]tyrosyl-tRNA synthetase and [Lys164]des-(321-419)tyrosyl-tRNA synthetase. Despite having only one binding site for tRNA, heterodimer has full aminoacylation activity at high concentrations of tyrosine. We have therefore produced a family of dimers that differ in stability near neutral pH. This novel approach using protein engineering allows specific dimerization of subunits of the same size that have different defined mutations, each subunit being tagged by the charge. Such hybrid proteins can be used to study subunit interaction.

Amino Acyl-tRNA Synthetases↗
PubMed1986

Characterisation of an mRNA encoding a human ribosomal protein homologous to the yeast L44 ribosomal protein.

We describe the isolation and characterisation of a full-length cDNA sequence (pZH-21) of a human ribosomal protein (rp) mRNA isolated from a cDNA library constructed from the human ZR-75-1 mammary tumour cell-line. The predicted protein is highly basic and shows 72% homology at the amino acid (aa) level with yeast rp L44. Comparative RNA blotting of ZR-75-1 poly(A)+ RNA isolated from cells cultured in the presence of the anti-oestrogen tamoxifen demonstrates the presence of a number of mRNA species whose concentration is elevated co-ordinately 5-6-fold in the presence of 17beta-oestradiol. Insulin in the presence of tamoxifen, also enhanced rp mRNA levels suggesting increased levels are a reflection of cell proliferation as opposed to specific hormonal regulation. Genomic analysis demonstrates the presence of a family of related human sequences, and homology with rat and guinea pig rp genes, but not yeast DNA. The conservation of rp aa sequence, in the absence of detectable homology at the nucleotide (nt) level, points to an important common functional role of the L44 protein in ribosome structure and function in man and yeast.

Amino Acid Sequence↗
PubMed1985

The significance of leptospiral titres associated with bovine abortion.

To investigate relationships between serological titres to 2 serovars, pomona (L. pomona) and hardjo (L. hardjo), of Leptospira interrogans and abortions, log linear and logit models were fitted to herd and individual cow data from cattle serologically negative for brucellosis. Serological titres to both serovars were significantly related to abortions in individual cows, with L. pomona having a stronger relationship than L. hardjo. L. hardjo was not significant when herd data were analysed. Differences between dairy and beef cattle in the serological titres found to both L. pomona and L. hardjo were detected when data sets of all cattle or cattle with no history of abortion were analysed. The beef/dairy differences may be due to different management practices and/or to different geographical distributions of both serovars and populations of beef and dairy cattle. If there are no cattle in a herd with a reciprocal titre of 3000 or greater for L. pomona, it is unlikely that L. pomona is associated with the abortion problem. There was no specific L. hardjo titre which separated high and low probabilities that the serum came from a cow or herd with an abortion history.

Abortion, Veterinary↗
PubMed1981

The hydrophobicities of cholera toxin, tetanus toxin and their components.

1. Charge-shift electrophoresis showed that cholera toxin and its subunits have no hydrophobic surfaces. 2. Amino-acid composition and sequence data suggested that the proteins have no masked hydrophobic regions. 3. The A subunit of cholera toxin may interact with polar molecules in the membrane to exert its effect inside the cell. 4. The only hydrophobic part of tetanus toxin was the H-chain.

Amino Acids↗
PubMed1980

Trichothiodystrophy: sulfur-deficient brittle hair as a marker for a neuroectodermal symptom complex.

Trichothiodystrophy, or sulfur-deficient brittle hair, is a clinical marker for a neuroectodermal symptom complex that usually features mental and physical retardation and may also include nail dystrophy, lamellar ichthyosis, ocular dysplasia, dental caries, and decreased fertility. Cystine-deficient hair is common to all patients. The hairs from two new patients were studied, and the most distinctive microscopic hair findings were striking bright and dark bands seen with polarizing microscopy using crossed polarizers. To date, all hair samples showing this banding have had an abnormally low sulfur content. Two-dimensional electrophoresis on the two protein fractions of the abnormal hair confirmed that the abnormality is caused by decreased synthesis of high-sulfur matrix proteins. Disturbances of the transport or utilization of sulfur-containing amino acids in other neuroectodermal tissues may be proposed to account for the various disease features in these persons.

Adult↗
PubMed1978

The prevalence and distribution of leptospiral titres in cattle and pigs in Queensland.

Serological test results for leptospiral species on serums from cattle and pigs performed by the diagnostic laboratories of the Queensland Department of Primary Industries from July 1973 to June 1976 were used to determine the prevalence and geographical distribution of 3 leptospiral serotypes in Queensland. There was a higher prevalence of antibodies to L. hardjo than to L. pomona in cattle, whereas in pigs the prevalence of antibodies to L. pomona was much higher than that for L. tarassovi or L. hardjo. Feral pigs had a particularly high prevalence of L. pomona antibodies. There is a different geographical distribution of antibodies to L. pomona and L. hardjo. L. hardjo antibodies appear to be fairly uniformly distributed but there is a higher prevalence of L. pomona antibodies in low rainfall areas. This relationship was shown to be significantly correlated.

Animals↗
PubMed1976

Infection and serological responses in cattle given 45/20 vaccine and later challenged with Brucella abortus.

One of 2 groups of 15 non-pregnant cows was vaccinated twice 6 weeks apart by the subcutaneous route with a killed adjuvant 45/20 vaccine. At the time of the first vaccination a bull was introduced for a period of 14 weeks. All animals were challenged with 1.5 x 10(7) Brucella abortus organisms given into the conjunctival sac 18 weeks after the second vaccination of the vaccinated group. The largest lesions at the site of vaccination (8 cm diam.) were seen 2 weeks after inoculation. Small lesions were still visible in 8 animals 1 year after vaccination. There was no appreciable serological response to the first vaccination. After the second vaccination some animals gave low positive titres, but all were serologically negative after 10 weeks. After challenge the highest complement fixation and standard agglutination tests were given by animals in the non-vaccinated group. Serum samples from 5 animals (2 vaccinated and 3 not vaccinated) showed a prozone effect at low dilution in the complement fixation test. In the non-vaccinated group 9 of the 15 cows became pregnant, 7 of which had weak calves or aborted and were shown to be infected with Br. abortus. The other 2, of which 1 was serologically positive, reared normal calves. Of the 10 vaccinated cows that became pregnant, 8 reared calves, 1 had a weak calf and the other aborted. These 2 cows and 1 other were infected. Considering the 11 infected pregnant animals 9 or 80 percent, lost their calves. The number of surviving calves was significantly higher in the vaccinated group indicating that the use of this 45/20 vaccine has considerable economic benefit. In each group 3 of the non-pregnant animals were infected.

Agglutination Tests↗