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Biomedical subjects

D A Matthews

Publications and source records attributed to D A Matthews.

At least 73 records · Page 4Linked to original sources
PubMed1991

Proteolytic release and crystallization of the RNase H domain of human immunodeficiency virus type 1 reverse transcriptase.

The RNase H domain of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase was released from recombinant DHFR-RNase H fusion protein by the action of HIV-1 protease and crystallized as large trigonal prisms that diffract x-rays to at least 2.4-A resolution. The protease cleavage occurred 18 residues away from the Phe440-Tyr441 site reported to be processed during maturation of the reverse transcriptase heterodimer. Mutagenesis of the protease-sensitive region (residues 430-440), which is part of the crystallized domain, indicates that any alteration of the wild-type sequence results in increased proteolysis of the p66 subunit. A model of asymmetric processing in HIV-1 reserve transcriptase which involves partial unfolding of the RNase H domain is proposed based on these results and the recently reported three-dimensional structure of this domain.

Amino Acid Sequence↗
PubMed1991

Crystal structure of the ribonuclease H domain of HIV-1 reverse transcriptase.

The crystal structure of the ribonuclease (RNase) H domain of HIV-1 reverse transcriptase (RT) has been determined at a resolution of 2.4 A and refined to a crystallographic R factor of 0.20. The protein folds into a five-stranded mixed beta sheet flanked by an asymmetric distribution of four alpha helices. Two divalent metal cations bind in the active site surrounded by a cluster of four conserved acidic amino acid residues. The overall structure is similar in most respects to the RNase H from Escherichia coli. Structural features characteristic of the retroviral protein suggest how it may interface with the DNA polymerase domain of p66 in the mature RT heterodimer. These features also offer insights into why the isolated RNase H domain is catalytically inactive but when combined in vitro with the isolated p51 domain of RT RNase H activity can be reconstituted. Surprisingly, the peptide bond cleaved by HIV-1 protease near the polymerase-RNase H junction of p66 is completely inaccessible to solvent in the structure reported here. This suggests that the homodimeric p66-p66 precursor of mature RT is asymmetric with one of the two RNase H domains at least partially unfolded.

Amino Acid Sequence↗
PubMed1991

Depression and somatization in the chronic fatigue syndrome.

PURPOSE: To report the prevalence, clinical features, and diagnostic associations of the proposed chronic fatigue syndrome (CFS) in a cohort of patients with chronic fatigue and to assess the usefulness of a structured psychiatric interview for detecting previously unrecognized psychiatric morbidity in patients with CFS. PATIENTS AND METHODS: A consecutive sample of 200 adult patients with a chief complaint of chronic fatigue was prospectively evaluated in a referral-based clinic within a university general medicine practice. All patients received a thorough medical history, physical examination, diagnostic laboratory testing, and portions of the Diagnostic Interview Schedule, version III-A. The criteria for CFS were applied, and patients with CFS were compared with matched control subjects from the inception cohort. RESULTS: The 60 patients with CFS had similar likelihoods of current psychiatric disorders (78% versus 82%), active mood disorders (73% versus 77%), and preexisting psychiatric disorders (42% versus 43%) when compared with fatigued control subjects. Patients with CFS were more likely to have somatization disorder (p less than 0.001) and to attribute their illness to a physical cause (p less than 0.005) than fatigued controls. Patients with CFS also displayed functional symptoms, often lifelong, which are not part of the case definition of CFS. Depressive features in patients with CFS were similar to those of control subjects, but a trend toward suicidal behavior was noted. CONCLUSIONS: Patients with CFS have a high prevalence of unrecognized, current psychiatric disorders, which often predate their fatigue syndrome. Assessment of patients with CFS should include a structured psychiatric evaluation.

Adult↗
PubMed1991

Role of aspartate-37 in determining cofactor specificity and binding in rat liver dihydropteridine reductase.

Full-length rat dihydropteridine reductase (DHPR) cDNAs have been combined with a prokaryotic expression vector and introduced into Escherichia coli. Transformed bacteria express dihydropteridine reductase immunoreactive proteins and demonstrate conversion of quinonoid dihydropteridines to their tetrahydro forms. Several recombinant enzymes have been purified to homogeneity and biochemical studies have been carried out comparing their properties with those exhibited by the rat liver enzyme. The optimal reaction conditions, kinetic constants, and stability are similar for the recombinant and naturally occurring enzyme. The results indicate that the nonmutant recombinant rat DHPR is an authentic replica of the natural protein and that the characteristics of DHPR activity are determined by a single gene product and do not require specific modification via the eukaryotic cell. In addition to the wild type, three specific mutagenic forms of the reductase, A-6-V, W-104-F, and D-37-I, and an additional abbreviated structure have also been formed. Each of the products exhibits reductase activity, although they show varied affinities for their cofactor, NADH, and less stability to chromatography, dialysis, and concentration than the wild-type enzyme. The N-terminal sequence contains a classic NADH binding region between amino acids 9 and 36, and Asp 37 is essential for binding the cofactor as is shown by the approximately 20-fold increase in dissociation constant for the D-37-I mutant and diminished kcat (approximately 43 s-1 compared to 156 s-1 for the wild-type enzyme). The results indicate that the DHPR cofactor binding site is similar to typical dinucleotide requiring dehydrogenases such as lactic acid and liver alcohol dehydrogenase.

Amino Acid Sequence↗
PubMed1991

The nucleotide sequences of intergenic regions between nine genes of pneumonia virus of mice establish the physical order of these genes in the viral genome.

We have cloned eight intergenic regions from the Pneumovirus pneumonia virus of mice that link the nine small and medium sized genes previously described (Chambers et al., 1990). The nucleotide sequences of the clones confirm the locations of these genes and their mRNA transcripts in the viral genome. The intergenic regions vary in size from 2-56 nucleotides and show only faint homology to each other or to their analogues in respiratory syncytial virus. Sequence alignments suggest that the location of the transcriptional start site for the mRNA encoding the major nucleocapsid protein of pneumonia virus of mice and respiratory syncytial virus may have altered during virus evolution by gain or loss of a transcriptional start signal.

Base Sequence↗
PubMed1991

Children in hospital: I. Survey of library and book provision.

Between 1989 and 1991 two related research projects were undertaken by the authors at the Department of Information and Library Studies, Aberystwyth, into services for children in hospital. This article summarizes the findings of the first of the projects, a survey of book and library services to children in hospital, giving a national profile of provision. It demonstrates a substantial provision of reading and other materials available to children in hospital but a small number of library services, as such. Nurses, teachers and hospital play staff generally exploited these materials for pleasure, educational and therapeutic purposes. The survey was based on questionnaires sent to all hospitals in the UK which treated children and was addressed, where possible, to hospital librarians, otherwise to the senior paediatric nurse. A shorter questionnaire was also addressed to all local authority Young People's and Schools Library services for a public library or school library perspective. Where there was evidence of the use of reading therapy, a further questionnaire was sent to explore its practice. A second article will discuss the results of the second project, which was devoted to a further exploration of reading therapy with children in hospital.

Bibliotherapy↗
PubMed1991

Evaluation and management of patients with chronic fatigue.

Chronic fatigue is a common and disabling problem in primary care practice. The differential diagnosis of chronic fatigue is extensive and includes medical disorders, altered physiologic states (eg, pregnancy, exertion), psychiatric disorders, lifestyle derangements, drugs, and controversial entities (eg, chronic candidiasis, food allergies, environmental illness, and chronic fatigue syndrome). The most common diagnoses are psychiatric disorders, including mood, anxiety, and somatoform disorders. A comprehensive approach to diagnosis and management is necessary, including structured psychiatric interviewing, functional assessment, and elicitation of the patient's diagnostic beliefs. Patients often believe they are suffering from an organic medical disorder (eg, viral or immunologic) and resist psychiatric labelling of their symptoms and referral to mental health practitioners. Establishing and maintaining rapport, having a flexible approach, and demonstrating a personal concern for the patient is essential. Drug therapy for specific psychiatric and medical illnesses and cognitive-behavioral approaches for enhancing coping mechanisms are effective.

Adult↗
PubMed1991

Panic disorder among patients with chronic fatigue.

Among 200 adults with a chief complaint of chronic fatigue evaluated in an internal medicine practice, currently active panic disorder was diagnosed in 26 patients (13%), a frequency tenfold greater than that in the general population. Panic disorder preceded or was coincidental with the onset of chronic fatigue in 21 of these patients. In comparison with the rest of the study cohort, significantly more patients with panic disorder had a history of severe depression, including persistent thoughts of death or suicide. Moreover, more patients with panic disorder showed a lifetime tendency to have physical symptoms that remained unexplained after medical evaluation. Our findings suggest that treatable panic disorder is an important contributor not only to major depression and somatization, but also to the etiology and clinical presentation of chronic fatigue in patients in an outpatient practice.

Adult↗
PubMed1991

Antibodies to Epstein-Barr virus in patients with chronic fatigue.

To clarify the role of Epstein-Barr virus (EBV) infection and the value of EBV antibody testing in evaluating patients with chronic fatigue, we studied 200 consecutive patients with chronic fatigue (mean duration, 9 years). Complete EBV serologic panels were obtained for 154 patients, 35 (23%) of whom met serologic or clinical criteria for chronic or reactivated EBV infection. We compared these patients with chronic EBV infection (CEBV cases) to 35 age- and sex-matched patients who were selected from the same cohort of fatigued patients but who did not meet the criteria (CEBV control subjects). We found few differences between groups in demographic characteristics, clinical features, and symptoms; CEBV cases were more likely to meet criteria for the proposed chronic fatigue syndrome (14% vs 0%), and to report that they suffered from an influenza-like illness at the onset of their fatigue syndrome (34% vs 12%), that they lost their job because of their fatigue (37% vs 11%), and that their fatigue was improved by recreational activity (26% vs 3%). Physical examination and laboratory testing showed few abnormalities in either group. Psychiatric morbidity was common in both groups, including mood disorders (63% of CEBV cases vs 54% of CEBV controls), anxiety (11% vs 9%) and somatization disorder (9% in each group). We conclude that EBV serologic patterns have little clinical usefulness in evaluating patients with chronic fatigue.

Adult↗
PubMed1991

Identification of variable domains of the attachment (G) protein of subgroup A respiratory syncytial viruses.

We have previously classified isolates from a respiratory syncytial (RS) virus epidemic into distinct lineages by restriction mapping and nucleotide sequencing of parts of the nucleocapsid protein and small hydrophobic protein genes, which are areas of the genome not considered to be under immunological pressure. This study has now been extended by the determination of the nucleotide sequences of the attachment (G) protein genes of isolates from each subgroup A lineage. Deduced amino acid identities of the G proteins ranged between 80% and 99%, corresponding closely to the previously determined relatedness of the lineages. The amino acid variability was not evenly distributed; in the extracellular part of the protein there was a sharply defined hypervariable domain which was separated from a more extended variable domain by a highly conserved region. Most nucleotide changes in the variable domains were in the first and second positions of the codon triplets. These results suggest that there may be considerable immunological pressure for change in certain areas of the G protein and this may account for the ability of this virus to reinfect individuals repeatedly. The results presented here reflect the pattern of published data comparing prototype strains of the A and B subgroups.

Amino Acid Sequence↗
PubMed1991

Substance use disorders in patients with chronic fatigue.

A high prevalence of mood disorders has been found among persons with chronic fatigue. The comorbidity of mood disorders and substance use disorders has long been recognized. In this study, the prevalence of substance use disorders among 100 patients with chronic fatigue was examined. Twenty-eight patients met DSM-III-R criteria for a lifetime diagnosis of substance abuse or dependence; ten of these patients had a current diagnosis. Forty-nine patients had no history of substance abuse or dependence but had other lifetime psychiatric diagnoses. Twenty-three patients had no history of substance abuse or psychiatric illness. No differences in demographic characteristics or in the features of chronic fatigue were found among the three groups. Patients with chronic fatigue who had a lifetime history of a substance use disorder reported more lifetime depressive symptoms and were more likely to have had suicidal ideation or attempts.

Adult↗
PubMed1991

Depression and chronic fatigue. Indications for psychiatric consultation.

Symptoms of fatigue and the fatigue syndrome itself are familiar complaints heard by nonpsychiatric physicians in the general hospital. The nature of these complaints is often diffuse and frequently conceals atypical psychiatric disorders. In the general hospital setting, consultation psychiatry, which functions as the interface between psychiatry and these medical practitioners, is ideally situated to assist in the assessment and management of these patients. This article reviews the methods of approach that psychiatric consultants can use to assist their nonpsychiatric colleagues in identification and referral for problems involving fatigue. In addition, a brief review of diagnosis, management, and treatment of such patients is given.

Adult↗
PubMed1990

Crystal structure of Escherichia coli thymidylate synthase containing bound 5-fluoro-2'-deoxyuridylate and 10-propargyl-5,8-dideazafolate.

The crystal structure of an Escherichia coli thymidylate synthase (TS) ternary complex containing 5-fluoro-2'-deoxyuridylate (FdUMP) and 10-propargyl-5,8-dideazafolate (PDDF) has been determined and refined at 2.3 A resolution. Each of the two chemically identical subunits folds into a three-layer domain anchored by a large six-stranded mixed beta-sheet. The backside of one sheet is juxtaposed against the corresponding face of the equivalent sheet in the second protomer creating a beta-sandwich. In contrast to other proteins of known structure in which aligned beta-sheets stack face to face with a counterclockwise rotation, sheets in the TS dimer are related by a clockwise twist. The substrate-binding pocket is a large funnel-shaped cleft extending some 25 A into the interior of each subunit and is surrounded by 30 amino acids, 28 from one subunit and two from the other. FdUMP binds at the bottom of this pocket covalently linked through C-6 to the sulfur of Cys146. Up-pointing faces of the pyrimidine and ribose rings are exposed to provide a complementary docking surface for the quinazoline ring of PDDF. The quinazoline inhibitor binds in a partially folded conformation with its p-aminobenzoyl glutamate tail exposed at the entrance to the active site cleft. Ternary complex formation is associated with a large conformational change involving four residues at the protein's carboxy terminus that close down on the distal side of the inhibitor's quinazoline ring, capping the active site and sequestering the bound ligands from bulk solvent.

Amino Acid Sequence↗
PubMed1990

Stereochemical mechanism of action for thymidylate synthase based on the X-ray structure of the covalent inhibitory ternary complex with 5-fluoro-2'-deoxyuridylate and 5,10-methylenetetrahydrofolate.

The structure of the Escherichia coli thymidylate synthase (TS) covalent inhibitory ternary complex consisting of enzyme, 5-fluoro-2'-deoxyuridylate (FdUMP) and 5,10-methylene tetrahydrofolate (CH2-H4PteGlu) has been determined at 2.5 A resolution using difference Fourier methods. This complex is believed to be a stable structural analog of a true catalytic intermediate. Knowledge of its three-dimensional structure and that for the apo enzyme, also reported here, suggests for the first time how TS may activate dUMP and CH2-H4PteGlu leading to formation of the intermediate and offers additional support for the hypothesis that the substrate and cofactor are linked by a methylene bridge between C-5 of the substrate nucleotide and N-5 of the cofactor. By correlating these structural results with the known stereospecificity of the TS-catalyzed reaction it can be inferred that the catalytic intermediate, once formed, must undergo a conformational isomerization before eliminating across the bond linking C-5 of dUMP to C-11 of the cofactor. The elimination itself may be catalyzed by proton transfer to the cofactor's 5 nitrogen from invariant Asp169 buried deep in the TS active site. The juxtaposition of Asp169 and bound tetrahydrofolate in TS is remarkably reminiscent of binding geometry found in dihydrofolate reductase where a similarly conserved carboxyl group serves as a general acid for protonating the corresponding pyrazine ring nitrogen of dihydrofolate.

Binding Sites↗
PubMed1990

Escherichia coli thymidylate synthase: amino acid substitutions by suppression of amber nonsense mutations.

By using site-directed oligonucleotide mutagenesis, amber nonsense stop codons (5'-TAG-3') have been introduced at 20 sites in the Escherichia coli thymidylate synthase gene. By transforming the thyA mutant plasmids into 13 strains, each of which harbor different amber suppressor tRNAs, we were able to generate over 245 amino acid substitutions in E. coli thymidylate synthase (EC 2.1.1.45). Growth characteristics of these mutants have been studied, yielding a body of information that includes some surprising results in light of the recently published crystal structure of the enzyme.

Amino Acid Sequence↗
PubMed1990

The low yield of physical examinations and laboratory investigations of patients with chronic fatigue.

Fatigue is a common symptom but guidelines for its appropriate evaluation are lacking. The authors prospectively studied 100 adults with a chief complaint of fatigue lasting at least 1 month in order to determine the diagnostic contribution of physical examinations and laboratory investigations. The evaluations were performed in the specialized clinic of a faculty practice. Physical examinations produced diagnostic information in 2% of patients, and laboratory investigations elucidated the cause of fatigue in 5% of patients. Structured follow-up evaluations after an average interval of 10 months failed to reveal any new organic causes for the fatigue symptom. Minor laboratory abnormalities were relatively common but did not contribute to the diagnostic process and did not seem to influence the clinical outcome. The authors conclude that the traditional medical evaluation of patients complaining of chronic fatigue has a low yield in discovering treatable physical disorders.

Adult↗
PubMed1990

How much practice makes perfect? A quantitative measure of the experience needed to achieve procedural competence.

Based on the general learning curve formula, the authors have devised a method to estimate the experience needed to achieve competence in the performance of medical and surgical procedures. The method quantitates the learning ability of the trainee, the technical difficulty of the procedure, and the expected level of competence. Two retrospective applications demonstrate the ease of use and reliability of the method.

Clinical Competence↗