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Biomedical subjects

L R Hoffman

Publications and source records attributed to L R Hoffman.

10 recordsLinked to original sources
PubMed1997

Structure-based identification of an inducer of the low-pH conformational change in the influenza virus hemagglutinin: irreversible inhibition of infectivity.

Past efforts to employ a structure-based approach to design an inhibitor of the fusion-inducing conformational change in the influenza virus hemagglutinin (HA) yielded a family of small benzoquinones and hydroquinones. The most potent of these, tert-butyl hydroquinone (TBHQ), inhibits both the conformational change in HA from strain X:31 influenza virus and viral infectivity in tissue culture cells with 50% inhibitory concentrations in the micromolar range (D. L. Bodian, R. B. Yamasaki, R. L. Buswell, J. F. Stearns, J. M. White, and I. D. Kuntz, Biochemistry 32:2967-2978, 1993). A new structure-based inhibitor design search was begun which involved (i) the recently refined crystal structure (2.1-A resolution) of the HA ectodomain, (ii) new insights into the conformational change, and (iii) improvements in the molecular docking program, DOCK. As a result, we identified new inhibitors of HA-mediated membrane fusion. Like TBHQ, most of these molecules inhibit the conformational change. One of the new compounds, however, facilitates rather than inhibits the HA conformational change. Nonetheless, the facilitator, diiodofluorescein, inhibits HA-mediated membrane fusion and, irreversibly, infectivity. We further characterized the effects of inhibitors from both searches on the conformational change and membrane fusion activity of HA as well as on viral infectivity. We also isolated and characterized several mutants resistant to each class of inhibitor. The implications of our results for HA-mediated membrane fusion, anti-influenza virus therapy, and structure-based inhibitor design are discussed.

Antiviral Agents↗
PubMed1996

Virus-cell and cell-cell fusion.

Significant progress has been made in elucidating the mechanisms of viral membrane fusion proteins; both those that function at low, as well as those that function at neutral, pH. For many viral fusion proteins evidence now suggests that a triggered conformational change that exposes a previously cryptic fusion peptide, along with a rearrangement of the fusion protein oligomer, allows the fusion peptide to gain access to the target bilayer and thus initiate the fusion reaction. Although the topologically equivalent process of cell-cell fusion is less well understood, several cell surface proteins, including members of the newly described ADAM gene family, have emerged as candidate adhesion/fusion proteins.

Cell Membrane↗
PubMed1992

Structure of N,N-[bis(2-pyridylmethyl)-gamma-aminobutyrato]copper(II) bromide methanol solvate.

[Cu(C16H18N3O2)]Br.CH4O, Mr = 459.83, orthorhombic, P2(1)2(1)2(1), a = 10.452 (4), b = 12.197 (7), c = 14.984 (6) A, V = 1910 (3) A3, Z = 4, Dm = 1.61 (1), Dx = 1.599 g cm-3, lambda(Mo K alpha) = 0.71073 A, mu = 32.37 cm-1, F(000) = 932, T = 174 K, R = 0.0396, wR = 0.0419, 1146 observed reflections [I greater than 3 sigma(I)]. The title compound is a polymeric species in the solid state, with a unit cell consisting of two segments of one-dimensional chains. The ligand, a derivative of gamma-aminobutyric acid in which the amino group is substituted with two 2-pyridylmethyl moieties, coordinates to one copper atom through the three nitrogen atoms and to another copper atom through the two carboxylate oxygen atoms. The copper(II) atom has a pseudo square-pyramidal geometry, distorted by a distant sixth interaction to a carboxylate oxygen atom [Cu-O(2), 2.770 (7) A].

Bromides↗
PubMed1992

Regional alterations in intestinal sucrase expression in streptozocin-treated chronically diabetic rats.

In ad libitum-fed diabetic rats, sucrase specific activities in jejunum and ileum were significantly increased two- to threefold compared to controls, a response unaltered by pair-feeding. Gradients of sucrase activities along the ileal villus-to-crypt axis were readily measured in crypt regions in diabetic, but not in nondiabetic, rats. Changes in sucrase activities were commensurate with increases in sucrase immunoreactivity and not a result of altered functional activity. Insulin treatment reversed these effects, although insulin-deficiency, studied in food-deprived, nondiabetic rats, did not affect sucrase expression. We conclude that chronic diabetes significantly stimulates sucrase expression along the proximal-to-distal and villus-to-crypt axes of rat small intestine. In ileum, these changes suggest marked alterations in phenotypic development of enterocytes along the villus-to-crypt axis. Alterations in sucrase expression do not appear to correlate with insulin states and are not a consequence of altered functional activity.

Adaptation, Physiological↗
PubMed1992

Altered regulation of regional sucrase-isomaltase expression in diabetic rat intestine.

Increased sucrase-isomaltase (SI) expression is a prominent feature of adaptive changes observed in the small intestine of streptozocin-treated chronically diabetic (CD) rats. In this study, we examine the cellular and molecular basis of increased SI expression in CD rats by determining SI specific activities and mRNA abundance in sequentially isolated enterocytes along the villus-to-crypt axis of proximal jejunum and distal ileum. In all regions, two- to fourfold increases in sucrase activity in diabetic rat enterocytes were paralleled by increases in SI mRNA. However, analogous to nondiabetic rat intestine, no differences in SI mRNA abundance were observed between corresponding enterocyte fractions from ileum and jejunum of diabetic rat intestine. By nuclear run-on assays, differences in rates of SI gene transcription were not observed in diabetic and nondiabetic intestinal tissues. We conclude that diabetes induces increased total and specific activities and mRNA abundance of intestinal SI, largely through the stabilization of SI mRNA. Furthermore, analogous to nondiabetic small intestine, differences in proximal-to-distal SI expression appear to be determined at the translational or posttranslational level.

Alkaline Phosphatase↗
PubMed1991

Determinants of regional sucrase-isomaltase expression in adult rat small intestine.

Sucrase-isomaltase (SI) expression along the longitudinal and vertical axis of the small intestine was studied by sequentially isolating enterocytes from villus to crypt of rat proximal jejunum and distal ileum. Gradients of sucrase activity were observed with greatest activity occurring in jejunal and villus regions. Along the villus-to-crypt axis, gradients of SI mRNA abundance corresponded with activity. However, along the longitudinal axis no differences in SI mRNA levels were observed, thus not accounting for the observed 3-5-fold difference in SI activities between jejunum and ileum. Comparison of SI immunoprecipitates from jejunal and ileal mucosal scrapings showed significant differences in gel mobilities of the more mature forms, which did not appear to affect SI functional activities. When relative rates of de novo SI protein synthesis were compared, [35S]methionine incorporation into all SI forms was observed to be 3-5-fold greater in jejunum than in ileum at all time points. Because these results suggested differences in regional translational regulation, subcellular distribution of SI mRNA in jejunal and ileal epithelial cells was compared. A greater proportion of jejunal SI mRNA was found to be associated with membrane-bound polyribosomes. We conclude 1) sucrase expression along the villus-to-crypt axis correlates with SI mRNA abundance, 2) post-translational processing of SI differ in ileum and jejunum, but appear not to determine SI expression, and 3) differences in translational processing in distal ileum and proximal jejunum may determine sucrase activity along the longitudinal axis of rat small intestine.

Animals↗