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Biomedical subjects

R A Grant

Publications and source records attributed to R A Grant.

15 recordsLinked to original sources
PubMed1992

Three-dimensional structure of Theiler virus.

Theiler murine encephalomyelitis virus strains are categorized into two groups, a neurovirulent group that rapidly kills the host, and a demyelinating group that causes a generally nonlethal infection of motor neurons followed by a persistent infection of the white matter with demyelinating lesions similar to those found in multiple sclerosis. The three-dimensional structure of the DA strain, a member of the demyelinating group, has been determined at 2.8 A resolution. As in other picornaviruses, the icosahedral capsid is formed by the packing of wedge-shaped eight-stranded antiparallel beta barrels. The surface of Theiler virus has large star-shaped plateaus at the fivefold axes and broad depressions spanning the twofold axes. Several unusual structural features are clustered near one edge of the depression. These include two finger-like loops projecting from the surface (one formed by residues 78-85 of VP1, and the other formed by residues 56-65 of VP3) and a third loop containing three cysteines (residues 87, 89, and 91 of VP3), which appear to be covalently modified. Most of the sequence differences between the demyelinating and neurovirulent groups that could play a role in determining pathogenesis map to the surface of the star-shaped plateau. The distribution of these sequence differences on the surface of the virion is consistent with models in which the differences in the pathogenesis of the two groups of Theiler viruses are the result of differences in immunological or receptor-mediated recognition processes.

Animals↗
PubMed1991

Analysis of symmetry and three-dimensional reconstruction of thin gp32*I crystals.

Thin, multilayered crystals of gp32*I were analyzed by negative stain electron microscopy and image processing. Images of untilted crystals exhibited different projection symmetries and structural motifs. Systematic analysis of these images categorized the projections into four types. Areas producing the type 1 projection were reconstructed in three-dimensions from four tilt series containing 111 images. The three-dimensional data has excellent p121 plane group symmetry and reveals that the gp32*I molecule contains two large domains linked together by a small domain. Computer simulations utilizing projection data suggested that the type 2 and 3 projections arise from superposition of type 1 projections related by a 21 screw axis along the projection axis. The three-dimensional reconstruction was utilized in a final simulation that explained the occurrence of the fourth type of projection. This work provides a firm foundation for future high-resolution analysis of the crystal by electron cryomicroscopy.

Crystallography↗
PubMed1979

Reconstruction of full-thickness loss skin wounds using skin collagen allografts.

Sheets of allogeneic dermal collagen measuring 20 X 15 mm and prepared by trypsin treatment of full-thickness skin were grafted under skin flaps in rats. After 2 to 5 weeks the protective recipient skin was excised and replaced by split-thickness skin isografts which remained viable on their supportive collagen beds. On average such composite grafts maintained 84 per cent of their original size over 3 to 28 weeks and in contrast with split-thickness skin grafts achieved full-thickness reconstruction of the excised skin.

Animals↗
PubMed1978

Nonreversible loss of platelet aggregability induced by calcium deprivation.

Platelets lose their ability to aggregate when deprived of divalent cations. This usually was studied by incubating human citrated platelet-rich plasma with EDTA or EGTA and then adding enough CaCl2 to combine with the chelating agent. Incubation for 5-7 min at 37 degrees C caused irreversible loss of the platelets' ability to adhere to glass and to aggregate with ADP, epinephrine, A23187, vasopressin, or serotonin or upon rewarming after chilling and markedly reduced aggregation with collagen or thrombin. Control samples incubated with saline, CaEDTA, or CaEGTA were not inhibited. Untreated platelets washed and incubated in solutions treated with resins that remove divalent cations lost their ability to aggregate in 30 min. More than about 0.26 mM Mg2+ partially protected the platelets. Unlike aggregation, ADP-induced shape change, clot retraction caused by thrombin or ADP plus reptilase, and thrombin-induced 14C-serotonin release were not inhibited after incubation. Aggregability was not restored by prolonged incubation with CaCl2, adding normal plasma, or washing the platelets. Its loss was temperature and pH dependent, occurring in 2 min at 43 degrees C but not in 7 min at 30 degrees C, and at pH 7.8 but much less at pH 7.2. The defect was not associated with an increase in platelet cyclic AMP, a decrease in metabolic ATP, or the presence of free ADP.

Calcium↗
PubMed1977

Incorporation of stored cell-free dermal collagen allografts into skin wounds: a short term study.

Allogeneic dermal collagen has been evaluated as an alternative to skin autografts for the permanent replacement of lost or damaged skin in the rat. All non-collagenous structures were removed from full-thickness back skin by treatment with a solution of crystalline trypsin. Such dermal collagen preparations were grafted into skin wounds, examined up to 8 1/2 weeks after operation, and compared with excised wounds and skin isografts and allografts of the same initial size. The dermal collagen grafts, particularly when dressed with a sheet of dermal collagen, become recellularised, revascularised and re-epidermalised. Unlike the skin allografts, there was no evidence of cellular rejection. Whereas contracture of the excised wounds was delayed, but not suppressed, by applying a conventional dressing, collagen grafts maintained from 60 to 100 per cent of their original size. In contrast, equivalent skin isografts shrank to 50-60 per cent and showed persistent epidermal hyperplasia.

Animals↗
PubMed1976

ADP-induced inhibition of von Willebrand factor-mediated platelet agglutination.

Human plasma von Willebrand factor (vWF) plus the antibiotic ristocetin, or bovine or porcine vWF alone, agglutinates platelets in either normal human ethylenediaminetetraacetate (EDTA)-treated citrated platelet-rich plasma (PRP) or citrated PRP from patients with the congenital platelet defect thrombasthenia. The prior addition of 1-10 muM ADP, which causes platelet shape change but not aggregation under these conditions, inhibited vWF-mediated agglutination. Inhibition was prevented by 200 muM ATP. Addition of ADP caused prompt reversal of established vWF-mediated agglutination, which resumed when the ADP was enzymatically removed. EDTA-treated, Formalin-fixed, washed normal platelets also underwent vWF-mediated agglutination. ADP was inhibitory only when added before fixation. Epinephrine (40 muM), prostaglandin E1 (7 muM), or serotonin (2 muM) added before fixation caused slight to moderate inhibition but always less than ADP. Platelets from blood chilled before fixation were fully active. Platelets fixed in freshly prepared PRP did not agglutinate as well as those fixed after incubation of PRP, probably because centrifugation exposes the platelets to ADP. It concluded that ADP causes a reversible decrease in the accessibility of the membrane receptor to vWF.

Adenosine Diphosphate↗
PubMedDate not supplied

Patch averaging of electron images of GP3*I crystals with variable thickness.

The combination of Fourier and correlation averaging techniques with multivariate statistical analysis and classification, a method known as patch averaging, is used to analyze untilted and tilted images of negatively stained GP32*I crystals, which exhibit variable thicknesses in a single crystal. Within a single image, coherent areas of the same apparent thickness can be distinguished from areas of differing thicknesses. Analysis using the phase relationships among symmetry-related reflections from reconstituted images obtained from untilted micrographs confirms the ability of the method to classify these variable thicknesses properly. Furthermore, the phases from some of the reconstituted images obtained from both untilted and tilted micrographs were found to match well with the phases in a previously determined three-dimensional data set of this crystal with pg symmetry along the crystallographic b axis. These results indicate the utility of the patch averaging procedures in the structural determination of protein crystals with different thicknesses.

Crystallization↗
PubMedDate not supplied

Histological studies of subcutaneous and intraperitoneal implants of trypsin-prepared dermal collagen allografts in the rat.

The possibility of using allograft collagen for the permanent replacement of lost or damaged connective tissues has been examined in the rat. The cellular components of skin, which are known to be of major importance in allograft rejection, were removed by treating skin with a solution of crystalline trypsin at 15 degrees C. Non-collagenous structures were largely removed by 7 days, but the purification process continued up to 28 days without damage to the collagen fibrils. Dermal collagen allografts, which were implanted intraperitoneally or subcutaneously and biopsied 3-83 days after operation, became recellularized and revascularized without being being resorbed. In contrast to skin allografts, there was no evidence of cellular rejection of the collagen grafts, even when recipient animals had been sensitized to allogeneic skin from the same donor. Densensitization of collagen to collagenase, by treating dermal collagen with solutions of glutaraldehyde at concentrations ranging from 0.001-1.0 per cent, was also investigated in vitro and by implantation. The best results, in terms of preservation of the collagen bundle architecture and graft recellularization without persisting inflammation, were achieved with collaged pre-treated with a solution of 0.01% glutaraldehyde.

Animals↗