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Biomedical subjects

S Knight

Publications and source records attributed to S Knight.

At least 19 recordsLinked to original sources
PubMed1995

Factors associated with lowered intelligence in homozygous sickle cell disease.

The intelligence quotient (IQ) of 60 patients with homozygous sickle cell (SS) disease and 60 age and sex matched controls with a normal haemoglobin (AA) genotype aged 15-18 years, followed up in a cohort study from birth, was assessed by the Wechsler intelligence scales for children or for adults. IQ appeared to be normally distributed in both genotypes but mean values in SS disease were 5.6 points (95% confidence interval (CI) 1.0 to 10.2) lower than in AA controls (p = 0.016). The difference occurred in both verbal (5.5 points, p = 0.017) and performance (5.0 points, p = 0.044) subscales of the IQ score and the IQ defect in SS disease was associated with a significantly lower attention factor score (p = 0.005) but not with other factor scores. The genotype difference in IQ was not accounted for by differences in parental occupational level, school absenteeism, or school drop out, or reported activity level. In SS disease, IQ was not related to mean steady state haemoglobin, fetal haemoglobin, or mean cell haemoglobin concentration, or clinical severity as judged by the frequency of painful crises, hospital admission, or sick visits. IQ, at age 15-18 years, correlated with the patients' height at all ages from 1 to 10 years (partial correlations increasing from 0.14 (p = 0.15) at age 1 to 0.27 (p = 0.004) at age 10). Adjusting for height reduced the mean genotype difference in IQ to 5.5 (95% CI 0.6 to 10.3) points at age 1 and to 2.6 points (95% CI to -2.3, 7.5) at age 10. Prepubertal height therefore accounted for much of the genotype difference in IQ. It is speculated that early factors, possible nutritional, contribute to both impaired growth and mental development in sickle cell disease.

Adolescent↗
PubMed1994

2.2 A resolution structure of the amino-terminal half of HIV-1 reverse transcriptase (fingers and palm subdomains).

BACKGROUND: HIV-1 reverse transcriptase (RT) catalyzes the transformation of single-stranded viral RNA into double-stranded DNA, which is integrated into host cell chromosomes. The molecule is a heterodimer of two subunits, p51 and p66. The amino acid sequence of p51 is identical to the sequence of the amino-terminal subdomains of p66. Earlier crystallographic studies indicate that the RT molecule is flexible, which may explain the difficulty in obtaining high-resolution data for the intact protein. We have therefore determined the structure of a fragment of RT (RT216), which contains only the amino-terminal half of the RT molecule ('finger' and 'palm' subdomains). RESULTS: The crystal structure of RT216 has been refined at 2.2 A resolution to a crystallographic R-value of 20.8%. The structure is very similar to that of the corresponding part of the p66 subunit in the p66/p51 heterodimer, although there is a small difference in the relative orientation of the two subdomains compared with the structure of an RT-DNA-antibody fragment complex. There are a large number of stabilizing contacts (mainly hydrogen bonds and hydrophobic interactions) between the subdomains. The locations of conserved amino acids and the position of some important drug-resistant mutations are described. CONCLUSIONS: The RT216 structure provides detailed three-dimensional information of one important part of HIV-1 RT (including the critical active site residues). We propose a model to explain the inhibitory effect of non-nucleoside inhibitors, which partially accounts for their effect in terms of conformational changes of active site residues.

Binding Sites↗
PubMed1992

Cefuroxime and cefuroxime axetil versus amoxicillin plus clavulanic acid in the treatment of lower respiratory tract infections.

In a large multinational study, the clinical and bacteriological efficacy of intravenous cefuroxime 750 mg t.i.d. followed by oral cefuroxime axetil 500 mg b.i.d. was compared to that of amoxicillin plus clavulanic acid (CA) administered as 1.2 g intravenously t.i.d. followed by 625 mg orally t.i.d. in the treatment of lower respiratory tract infections in hospitalised patients. A total of 512 patients were entered (256 in each treatment group). All were suffering from pneumonia or acute exacerbations of chronic bronchitis or bronchiectasis and required initial parenteral antibiotic therapy. Parenteral therapy lasted 48 to 72 h and was followed by five days of oral therapy. The clinical responses in the two treatment groups were very similar: 223 of 256 (87.1%) patients were cured or improved with cefuroxime/cefuroxime axetil compared to 220 of 256 (85.9%) with amoxicillin/CA. Positive pre-treatment sputum samples were obtained from 44% of the patients. Clearance rates obtained were again similar: 72.8% with cefuroxime/cefuroxime axetil and 70% with amoxicillin/CA. Ten percent of the isolates were beta-lactamase producers, similar numbers of which were cleared in both groups. Both regimens were generally well tolerated, with only 5% of patients treated with the cefuroxime regimen and 4.3% of patients treated with amoxicillin/CA experiencing drug-related adverse events. Cefuroxime/cefuroxime axetil "follow-on" therapy produces clinical and bacteriological efficacy equivalent to that of amoxicillin/CA, with the advantage of twice daily oral administration.

Administration, Oral↗
PubMed1990

Crystallographic analysis of ribulose 1,5-bisphosphate carboxylase from spinach at 2.4 A resolution. Subunit interactions and active site.

The X-ray structure of the quaternary complex of ribulose 1,5-bisphosphate carboxylase/oxygenase from spinach with CO2, Mg2+ and a reaction-intermediate analogue (CABP) has been determined and refined at 2.4 A resolution. Cyclic non-crystallographic symmetry averaging around the molecular 4-fold axis and phase combination were used to improve the initial multiple isomorphous replacement phases. A model composed of one large subunit and one small subunit was built in the resulting electron density map, which was of excellent quality. Application of the local symmetry gave an initial model of the L8S8 molecule with a crystallographic R-value of 0.43. Refinement of this initial model was performed by a combination of conventional least-squares energy refinement and molecular dynamics simulation using the XPLOR program. Three rounds of refinement, interspersed with manual rebuilding at the graphics display, resulted in a model containing all of the 123 amino acid residues in the small subunit, and 467 of the 475 residues in the large subunit. The R-value for this model is 0.24, with relatively small deviations from ideal stereochemistry. Subunit interactions in the L8S8 molecule have been analysed and are described. The interface areas between the subunits are extensive, and bury almost half of the accessible surface areas of both the large and the small subunit. A number of conserved interaction areas that may be of functional significance have been identified and are described, and biochemical and mutagenesis data are discussed in the structural framework of the model.

Amino Acid Sequence↗
PubMed1990

Comparison of the crystal structures of L2 and L8S8 Rubisco suggests a functional role for the small subunit.

Comparison of the crystal structures of the L2 and L8S8 forms of ribulose-1,5-bisphosphate carboxylase from Rhodospirillum rubrum and spinach respectively, reveals a remarkable similarity in the overall architecture of the L2 building blocks in the two enzymes. Within the L subunits, no large conformational differences such as domain-domain rotations were found. In spite of a somewhat different packing of the L subunits in the L2 dimer, the active sites of the two enzymes are highly conserved. Significant local conformational differences are, however, observed for the C-terminal part of the polypeptide chains as well as for loop 7, helix alpha 7, loop 8 and helix alpha 8 in the barrel domain. The small subunit forms extensive interactions with one of these alpha helices, alpha 8, in the spinach L8S8 enzyme. The loops are at the active site and one of them forms a phosphate binding site for the substrate. We suggest that the small subunit modulates substrate binding and, possibly, the carboxylation/oxygenation ratio by inducing conformational changes in the active site through interactions distant from this site.

Amino Acid Sequence↗
PubMed1990

Retrophrenic location of the internal mammary artery graft.

A technique of locating the internal mammary artery behind the phrenic nerve is described, which extends the application of internal mammary artery grafting to the lateral wall of the left ventricle. The technique also facilitates the performance of the posterolateral anastomosis between the internal mammary and circumflex coronary arteries.

Humans↗
PubMed1990

Residues in three conserved regions of the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase are required for quaternary structure.

To explore the role of individual residues in the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39), small subunits with single amino acid substitutions in three regions of relative sequence conservation were produced by directed mutagenesis of the rbcS gene from Anabaena 7120. These altered small subunits were cosynthesized with large subunits (from an expressed Anabaena rbcL gene) in Escherichia coli. Mutants were analyzed for effects on quaternary structure and catalytic activity. Changing Glu-13S (numbering used is that of the spinach enzyme) to Val, Trp-67S to Arg, Pro-73S to His, or Tyr-98S to Asn prevented accumulation of stable holoenzyme. Interpretation of these results using a model for the three-dimensional structure of the spinach enzyme based on x-ray crystallographic data suggests that our small subunit mutants containing substitutions at positions 13S and 67S probably do not assemble because of mispairing or nonpairing of charged residues on the interfacing surfaces of the large and small subunits. The failure of small subunits substituted at positions 73S or 98S to assemble correctly may result from disruption of intersubunit or intrasubunit hydrophobic pockets, respectively.

Amino Acid Sequence↗
PubMed1990

Analysis of very late gene expression by Autographa californica nuclear polyhedrosis virus and the further development of multiple expression vectors.

The consequences of locating the polyhedrin gene coding sequences and the p10 promoter at heterologous positions within the Autographa californica nuclear polyhedrosis virus (AcMNPV) genome were investigated. Positioning the polyhedrin or beta-galactosidase coding sequences under the control of the p10 gene promoter via the use of the new transfer vector, pAcUW1, resulted in viable recombinant viruses able to produce high levels of each non-fused gene product at the appropriate time. Polyhedra were also produced by the virus with the p10 promoter-polyhedrin hybrid gene and appeared normal in thin sections. Therefore the combination of polyhedrin promoter and coding sequences is evidently not essential for efficient expression of this protein. The p10 promoter can serve this function equally well. Viruses with the p10 promoter and beta-galactosidase coding sequences placed upstream from the polyhedrin gene in either orientation produced large amounts of beta-galactosidase protein in infected cells, thus demonstrating that the p10 promoter can function at an alternative position within the virus genome. A second transfer vector, pAcUW2B, was constructed, with a copy of the p10 gene promoter placed upstream and in opposition to the polyhedrin gene. This mediates the insertion of any foreign gene under the control of the p10 promoter while preserving normal p10 gene expression. The advantages of these constructs over the conventional vectors presently used to express foreign genes in insect cell systems and their utilization in the production of virus insecticides are discussed.

Animals↗
PubMed1990

Muramic acid is not detectable in Chlamydia psittaci or Chlamydia trachomatis by gas chromatography-mass spectrometry.

By using the powerful separation technique of capillary gas chromatography combined with the selectivity of mass spectrometric detection, muramic acid was not detectable in purified elementary bodies of Chlamydia psittaci Cal 10 (less than or equal to 0.006%) or C. trachomatis serovar E (less than or equal to 0.02%). This confirms previous reports which suggested the absence of a typical peptidoglycan in Chlamydia spp.

Chlamydia trachomatis↗
PubMed1989

Isolation of a gene that down-regulates nitrate assimilation and influences another regulatory gene in the same system.

Glutamine is the preferred source of nitrogen of Neurospora crassa. In its presence and that of the gene product of MS5 (nmr-1), the fungus represses the assimilation of less preferred forms of nitrogen, such as nitrate. In the absence of glutamine and the presence of the product of gene nit-2, less preferred forms of nitrogen are assimilated as long as a specific pathway for their assimilation is induced. We report here the isolation, from a cosmid bank, of a gene that complements MS5 and can also complement nit-2. We speculate that this result suggests an interaction between the MS5 and nit-2 gene products and that this is important in the regulation of nitrate assimilation.

Cosmids↗
PubMed1987

Silent partners: the wives of sleep apneic patients.

The wives of 10 male patients being treated for sleep apnea, obstructive type, were interviewed and given the Social Adjustment Scale (SAS) and Marital Satisfaction Inventory (MSI). The patients also completed an SAS and a Minnesota Multiphasic Personality Inventory (MMPI). These data were compared with those from a sample of divorced patients from the same pool. The married patients were significantly more depressed and socially isolated than were those divorced. Both marital partners showed poor adjustment in the Marital and Social/Leisure areas, and patients also showed poor adjustment in their Parental Role. Marriages do not necessarily represent social support but appear to be an added burden for sleep apneic patients.

Adult↗
PubMed1985

Active site specific cadmium(II)-substituted horse liver alcohol dehydrogenase: crystal structures of the free enzyme, its binary complex with NADH, and the ternary complex with NADH and bound p-bromobenzyl alcohol.

Three crystal structures have been determined of active site specific substituted Cd(II) horse liver alcohol dehydrogenase and its complexes. Intensities were collected for the free, orthorhombic enzyme to 2.4-A resolution and for a triclinic binary complex with NADH to 2.7-A resolution. A ternary complex was crystallized from an equilibrium mixture of NAD+ and p-bromobenzyl alcohol. The microspectrophotometric analysis of these single crystals showed the protein-bound coenzyme to be largely NADH, which proves the complex to consist of CdII-LADH, NADH, and p-bromobenzyl alcohol. Intensity data for this abortive ternary complex were collected to 2.9-A resolution. The coordination geometry in the free Cd(II)-substituted enzyme is highly similar to that of the native enzyme. Cd(II) is bound to Cys-46, Cys-174, His-67, and a water molecule in a distorted tetrahedral geometry. Binding of coenzymes induces a conformational change similar to that in the native enzyme. The interactions between the coenzyme and the protein in the binary and ternary complexes are highly similar to those in the native ternary complexes. The substrate binds directly to the cadmium ion in a distorted tetrahedral geometry. No large, significant structural changes compared to the native ternary complex with coenzyme and p-bromobenzyl alcohol were found. The implications of these results for the use of active site specific Cd(II)-substituted horse liver alcohol dehydrogenase as a model system for the native enzyme are discussed.

Alcohol Dehydrogenase↗