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Biomedical subjects

H A Lewis

Publications and source records attributed to H A Lewis.

At least 19 recordsLinked to original sources
PubMed2005

Structural analysis of a set of proteins resulting from a bacterial genomics project.

The targets of the Structural GenomiX (SGX) bacterial genomics project were proteins conserved in multiple prokaryotic organisms with no obvious sequence homolog in the Protein Data Bank of known structures. The outcome of this work was 80 structures, covering 60 unique sequences and 49 different genes. Experimental phase determination from proteins incorporating Se-Met was carried out for 45 structures with most of the remainder solved by molecular replacement using members of the experimentally phased set as search models. An automated tool was developed to deposit these structures in the Protein Data Bank, along with the associated X-ray diffraction data (including refined experimental phases) and experimentally confirmed sequences. BLAST comparisons of the SGX structures with structures that had appeared in the Protein Data Bank over the intervening 3.5 years since the SGX target list had been compiled identified homologs for 49 of the 60 unique sequences represented by the SGX structures. This result indicates that, for bacterial structures that are relatively easy to express, purify, and crystallize, the structural coverage of gene space is proceeding rapidly. More distant sequence-structure relationships between the SGX and PDB structures were investigated using PDB-BLAST and Combinatorial Extension (CE). Only one structure, SufD, has a truly unique topology compared to all folds in the PDB.

Databases, Protein↗
PubMed2004

Oral health knowledge and original practices of African traditional healers in Zonkizizwe and Dube, South Africa.

Self reported oral health knowledge and practices of 83 traditional healers in Zonkizizwe (56) and Dube (27) Gauteng Province, South Africa were carried out using a questionnaire and clinical photographs of common oral conditions. The mean age for the total group was 49.5 with 35 males and 48 females. Although only 17 of the healers were members of a professional association, many indicated their willingness to join one. 40 (71%) of healers in Zonkizizwe kept written client records but far fewer 3 (11%) did so in Dube. More than 90% of traditional healers from both areas correctly identified photographs of gingival inflammation, dental caries and oral candidiasis. Over 50% of healers from both areas had patients who presented with mouth problems. Ninety percent of healers in Zonkizizwe referred patients to the formal health care sector but less than 50% in Dube did so. A vast majority of healers gave oral health advice to their patients, many of whom gave specific tooth brush instruction. The study provides an initial understanding of the practices of healers regarding oral health.

Adolescent↗
PubMed2001

A structural genomics approach to the study of quorum sensing: crystal structures of three LuxS orthologs.

BACKGROUND: Quorum sensing is the mechanism by which bacteria control gene expression in response to cell density. Two major quorum-sensing systems have been identified, system 1 and system 2, each with a characteristic signaling molecule (autoinducer-1, or AI-1, in the case of system 1, and AI-2 in system 2). The luxS gene is required for the AI-2 system of quorum sensing. LuxS and AI-2 have been described in both Gram-negative and Gram-positive bacterial species and have been shown to be involved in the expression of virulence genes in several pathogens. RESULTS: The structure of the LuxS protein from three different bacterial species with resolutions ranging from 1.8 A to 2.4 A has been solved using an X-ray crystallographic structural genomics approach. The structure of LuxS reported here is seen to have a new alpha-beta fold. In all structures, an equivalent homodimer is observed. A metal ion identified as zinc was seen bound to a Cys-His-His triad. Methionine was found bound to the protein near the metal and at the dimer interface. CONCLUSIONS: These structures provide support for a hypothesis that explains the in vivo action of LuxS. Specifically, acting as a homodimer, the protein binds a methionine analog, S-ribosylhomocysteine (SRH). The zinc atom is in position to cleave the ribose ring in a step along the synthesis pathway of AI-2.

Amino Acid Sequence↗
PubMed2000

The tetranucleotide UCAY directs the specific recognition of RNA by the Nova K-homology 3 domain.

The Nova family of proteins are target antigens in the autoimmune disorder paraneoplastic opsoclonus-myoclonus ataxia and contain K-homology (KH)-type RNA binding domains. The Nova-1 protein has recently been shown to regulate alternative splicing of the alpha2 glycine receptor subunit pre-mRNA by binding to an intronic element containing repeats of the tetranucleotide UCAU. Here, we have used selection-amplification to demonstrate that the KH3 domain of Nova recognizes a single UCAY element in the context of a 20-base hairpin RNA; the UCAY tetranucleotide is optimally presented as a loop element of the hairpin scaffold and requires protein residues C-terminal to the previously defined KH domain. These results suggest that KH domains in general recognize tetranucleotide motifs and that biological RNA targets of KH domains may use either RNA secondary structure or repeated sequence elements to achieve high affinity and specificity of protein binding.

Amino Acid Motifs↗
PubMed2000

Sequence-specific RNA binding by a Nova KH domain: implications for paraneoplastic disease and the fragile X syndrome.

The structure of a Nova protein K homology (KH) domain recognizing single-stranded RNA has been determined at 2.4 A resolution. Mammalian Nova antigens (1 and 2) constitute an important family of regulators of RNA metabolism in neurons, first identified using sera from cancer patients with the autoimmune disorder paraneoplastic opsoclonus-myoclonus ataxia (POMA). The structure of the third KH domain (KH3) of Nova-2 bound to a stem loop RNA resembles a molecular vise, with 5'-Ura-Cyt-Ade-Cyt-3' pinioned between an invariant Gly-X-X-Gly motif and the variable loop. Tetranucleotide recognition is supported by an aliphatic alpha helix/beta sheet RNA-binding platform, which mimics 5'-Ura-Gua-3' by making Watson-Crick-like hydrogen bonds with 5'-Cyt-Ade-3'. Sequence conservation suggests that fragile X mental retardation results from perturbation of RNA binding by the FMR1 protein.

Amino Acid Motifs↗
PubMed1999

Crystal structures of Nova-1 and Nova-2 K-homology RNA-binding domains.

BACKGROUND: Nova-1 and Nova-2 are related neuronal proteins that were initially cloned using antisera obtained from patients with the autoimmune neurological disease paraneoplastic opsoclonus-myoclonus ataxia (POMA). Both of these disease gene products contain three RNA-binding motifs known as K-homology or KH domains, and their RNA ligands have been identified via binding-site selection experiments. The KH motif structure has been determined previously using NMR spectroscopy, but not using X-ray crystallography. Many proteins contain more than one KH domain, yet there is no published structural information regarding the behavior of such multimers. RESULTS: We have obtained the first X-ray crystallographic structures of KH-domain-containing proteins. Structures of the third KH domains (KH3) of Nova-1 and Nova-2 were determined by multiple isomorphous replacement and molecular replacement at 2.6 A and 2.0 A, respectively. These highly similar RNA-binding motifs form a compact protease-resistant domain resembling an open-faced sandwich, consisting of a three-stranded antiparallel beta sheet topped by three alpha helices. In both Nova crystals, the lattice is composed of symmetric tetramers of KH3 domains that are created by two dimer interfaces. CONCLUSIONS: The crystal structures of both Nova KH3 domains are similar to the previously determined NMR structures. The most significant differences among the KH domains involve changes in the positioning of one or more of the alpha helices with respect to the betasheet, particularly in the NMR structure of the KH1 domain of the Fragile X disease protein FMR-1. Loop regions in the KH domains are clearly visible in the crystal structure, unlike the NMR structures, revealing the conformation of the invariant Gly-X-X-Gly segment that is thought to participate in RNA-binding and of the variable region. The tetrameric arrangements of the Nova KH3 domains provide insights into how KH domains may interact with each other in proteins containing multiple KH motifs.

Amino Acid Sequence↗
PubMed1999

An oral health promotion module for the primary health care nursing course in Acornhoek, South Africa.

The severe personnel shortage in the health professions in most developing communities is well documented. This dearth of health workers and the widespread adoption of the primary health care approach (PHCA), requires that health professionals be trained to understand and effectively utilize the skills offered by other disciplines in the health care field. Nurses are expected to play active roles in the promotion of health including oral health, particularly in the rural under-served communities. There is a paucity of oral health education in nursing curricula. This article describes a 4-day module on oral health promotion developed and delivered to 36 nurses as part of a 12-month primary health care nursing (PHCN) training course. The module utilized a variety of educational methods and materials to facilitate and encourage both individual and group learning. The module was evaluated using both student academic attainment and perceptions as outcome measures. The evaluation and the experience of facilitating this module show that an oral health promotion module of short duration can sensitize nurses to the importance of oral health and increase oral health knowledge and skills.

Curriculum↗
PubMed1998

Genotoxicity from domestic use of organophosphate pesticides.

This report describes the types of chromosome damage in peripheral blood found in patients exposed to domestic application of organophosphate pesticides. These changes serve as a biomarker of cumulative toxic exposure. Susceptible individuals show DNA damage as chromosome alterations. The importance of these findings is that the apparent genotoxic changes occurred from domestic application of two of the commonly used organophosphate pesticides in America and adds one more adverse potential effect from these hazardous chemicals. Peripheral blood from eight patients exposed to the domestic spraying of organophosphate pesticides was cultured and the chromosomes photographed. The types of chromosome alterations seen included chromatid and chromosome breaks, single and double minutes, dicentrics, rings, translocations, exchanges (including sister chromatid), and endoreduplications. Our findings support previous findings that organophosphate pesticides have genotoxic effects even at domestically sprayed levels.

Accidents, Home↗
PubMed1996

Hope, coping, and adjustment among children with sickle cell disease: tests of mediator and moderator models.

Tested mediator and moderator models of hope, coping, and adjustment in 39 children with sickle cell disease. In home interviews parents provided information on demographics and functional adjustment. Children self-reported levels of hope, coping strategies, and psychological adjustment. Coping strategies moderated, but did not mediate, the relationship between hope and adjustment. Hope was negatively associated with anxiety when active coping, support coping, and distraction coping was high. Avoidance coping did not moderate the hope-adjustment relationship but was positively related to anxiety. No effects were found for depressive symptoms or for the functional measures of adjustment.

Adaptation, Psychological↗
PubMed1996

The effectiveness of a school-based fluoride mouth rinse programme.

The objective of this study was to determine the effectiveness of unsupervised weekly fluoride mouth rinsing (FMR) with 10 mls of 0.2 per cent sodium fluoride on the caries increment of permanent teeth in schoolchildren aged 6-12 years over a 3 year period. Caries was assessed using DMFT and DMFS indices (WHO, 1987). Over 2000 children from 4 schools in the Johannesburg area were selected at baseline. For analysis purposes pupils were pooled into 2 groups, those who received and those who did not receive the FMR. There were significant differences in mean decayed scores after 3 years. The percentage caries reduction achieved with the FMR was approximately 15 per cent. Reductions of up to 30 per cent have been recorded in previous studies of this nature. The overall caries reduction for this study period can be considered low.

Analysis of Variance↗
PubMed1995

Prevalence and severity of fluorosis in the primary and permanent dentition using the TSIF.

This paper reports on the prevalence and severity of dental fluorosis in the primary and permanent teeth and the tooth surfaces of 262 school children aged 6-18 years from two communities in KwaNdebele (South Africa), the first with 8-9 ppm F-, and the second with 0.6-1.6 ppm F- in the drinking water. The Tooth Surface Index of Fluorosis (TSIF) was used to measure the degree of fluorosis. In both areas, the population prevalence, for primary and permanent teeth was more than 90 per cent. For the lower F- area, 40 per cent of tooth surfaces were free of fluorosis compared with only 22 per cent in the high F- area. Of the surfaces affected by fluorosis in the high F- area, 37 per cent scored in the categories 4-7, compared with 6 per cent in the lower F- area. This difference in severity was found to be statistically significant (P<0.001). This study has shown that, in two areas with significantly different levels of fluoride in the water supply, the population prevalences of fluorosis were similar, but significant differences existed in severity. The World Health Organization 1984 guidelines for Drinking-water Quality recommend that 1.5 ppm F- is the maximum acceptable concentration in drinking water but this may not be appropriate for South Africa.

Adolescent↗
PubMed1992

A mobile dental system in southern Africa.

Recent studies indicate a great need for dental treatment and preventive services in dentally underserved communities in southern Africa. Geographic inaccessibility, limited financial resources, and a maldistribution of dental personnel are the main barriers to oral health care. This project describes the evolution and utilization of a unique, purpose-built, mobile dental unit (MDU). From a compact 2 x 2.5 meter box trailer, an enclosed area of 8 x 9 meters is formed by deploying a cover system housed on top of the trailer. Once deployed, the unit becomes four fully equipped dental operatories and a combined waiting and educational area, with all-weather protection. Comprehensive care is provided by dental auxiliaries. The underlying philosophy of the service is based on the primary oral health care approach. To date, the MDU has visited a wide variety of rural and urban communities where several thousand patients have been examined and treated. Assessment of the MDU indicates that it is an effective and viable alternative oral health delivery system.

Adolescent↗
PubMed1990

Suitability of nurses and school-teachers as oral health educators in Gazankulu--a pilot study.

This study investigated the suitability of nurses and teachers as potential oral health educators. The assessment was based on a concept of suitability that embraced biological and psycho-social variables. These included oral health status, knowledge, attitudes and reported oral health behaviour. The study population comprised 48 nurses and 43 school-teachers. DMFT of nurses was 4, 6 and teachers 2,5. More than 80 percent of both groups required some form of periodontal treatment. An adequate but basic knowledge of the causes and prevention of oral disease was demonstrated. More that 50 percent of both groups did not visit a dentist annually. Attitudes reflected the belief that teeth are expendable and easily replaceable. In terms of the theoretical model these nurses and teachers do not meet all the criteria that define "suitable" oral health educators. The findings of the present study have provided a profile which has highlighted certain deficiencies in knowledge, attitudes and behaviour. Further research using this model requires the inclusion of motivational and interest variables.

Adult↗
PubMed1989

Racial classification in dental literature: is it always necessary?

The purpose of the present study is to describe and analyse the use of terms (black, coloured, white, indian, african and non-white) that classify people for research purposes along racial lines. All scientific articles published in the Journal of the Dental Association of South Africa, from Jan 1979 to Dec 1988, were reviewed. Of the 493 articles covered, 92 made use of one or more of the terms, and 10 (11 per cent) either explained, defined, referenced and/or justified their use, while 09 per cent of the articles did not do so. Based on these reviews, it may be concluded that the use of these terms is not always necessary or justified and can reinforce thinking in racial rather than in social and behavioural terms. The unjustified usage of racial variables may limit our theoretical perspectives and lead us into questionable research.

Humans↗