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Biomedical subjects

A McPherson

Publications and source records attributed to A McPherson.

At least 91 records · Page 5Linked to original sources
PubMed1996

Incorporation of microcrystals by growing protein and virus crystals.

In the course of time-lapse video and atomic force microscopy (AFM) investigations of macromolecular crystal growth, we frequently observed the sedimentation of microcrystals and three-dimensional nuclei onto the surfaces of much larger, growing protein or virus crystals. This was followed by the direct incorporation over time of the smaller crystals into the bulk of the larger crystals. In some cases, clear indications were present that upon absorption of the small crystal onto the surface of the larger, there was proper alignment of the respective lattices, and consolidation proceeded without observable defect formation, i.e., the two lattices knitted together without discontinuity. In the case of at least one virus crystal, cubic satellite tobacco mosaic virus (STMV), addition of three-dimensional nuclei and subsequent expansion provided the principal growth mechanism at high supersaturation. This process has not been reported for growth from solution of conventional crystals. In numerous other instances, the lattices of the small and larger crystals were obviously misaligned, and incorporation occurred with the formation of some defect. This phenomenon of small crystals physically embedded in larger crystals could only degrade the overall diffraction and materials properties of macromolecular crystals.

Crystallization↗
PubMed1996

Treating bulimia nervosa in primary care: a pilot study.

OBJECTIVE: To develop and evaluate a simplified and condensed cognitive behavioral treatment for bulimia nervosa suitable for use in primary care. METHOD: Once developed, the treatment was tested on a consecutive series of 11 patients. RESULTS: Six patients did well, 3 were nonresponders, and in the other 2 external events interfered with progress. DISCUSSION: This form of treatment may benefit a significant proportion of those patients with bulimia nervosa who are seen in primary care. It can be administered by nonspecialist therapists.

Adolescent↗
PubMed1996

Crystal structure of turnip yellow mosaic virus.

The structure of turnip yellow mosaic virus (TYMV) has been solved to 3.2 A resolution and an R-value of 18.7%. The structure is consistent with models based on low resolution X-ray and electron microscopy studies, with pentameric and hexameric protein aggregates protruding from the surface and forming deep valleys at the quasi three-fold axes. The N-terminal 26 residues of the A-subunit are disordered, while those of the B- and C-subunits are seen to interact around the interior of the quasi six-fold cluster where they form an annulus. The three histidine residues of each protein subunit are located in the interior and accessible for interaction with the RNA genome. The appearance of the interior surface of the virus capsid, along with buried surface area calculations, suggest that a pentameric unit is lost during decapsidation.

Amino Acid Sequence↗
PubMed1996

The important attributes of a nurse from the perspective of qualified and student nurses.

The studies described here set out to discover what student and qualified nurses understand to be the important attributes of a nurse. The first study was exploratory and used a repertory grid technique to ask 72 students, qualified nurses and nurse lecturers to compare themselves (as a nurse) with a number of other nurses and carers of their own choosing. The constructs that the participants used to make these comparisons were then categorized into attributes. Those attributes that had been used by more than 10% of any of the subgroups were used in the second study as the basis of a questionnaire in which nurses were asked to put these categories in order of importance. The questionnaire was completed by 565 qualified and student nurses. The responses showed a remarkable level of agreement between nurses, irrespective of rank or student status. The only attribute over which there were large differences was intelligence. The study provides strong evidence that the view of the important attributes of a nurse remain unchanged right across the nursing profession, and the discovery of these attributes has important implications for nurse selection and training.

Adult↗
PubMed1995

Structural comparison of the plant satellite viruses.

Detailed structures are now available for three plant satellite viruses, satellite tobacco necrosis virus (STNV), satellite tobacco mosaic virus (STMV), and satellite panicum mosaic virus (SPMV). It is, therefore, possible to compare the tertiary structure of viral protein subunits, their quaternary interactions, and the interactions of protein subunits with the RNA genome. This analysis indicates that, in spite of common function and preservation of a "jelly-roll" motif in the protein monomer, the three viruses are remarkably different. The differences include the arrangement of secondary structural elements, interactions of adjacent subunits, and the disposition of subunits relative to icosahedral symmetry axes. In each of the three viruses, however, the narrow end of the jelly roll forms fivefold contacts. The fivefold protein interactions are organized about a Ca2+ ion for STNV, an anion for STMV, and, apparently, neither of these for SPMV. Low-resolution neutron diffraction studies using H2O/D2O solvent contrast variation revealed the general location of the RNA genome within the STNV. In the case of SPMV, regions of electron density on the interior of the capsid could be assigned to RNA, although it was not possible to model the nucleic acid. Only for STMV was nucleic acid visible in election density maps, and this was manifested as double-helical RNA segments associated with each coat protein dimer. The observations presented here provide no support for any common evolutionary relationship.

Amino Acid Sequence↗
PubMed1995

Determination of local refractive index for protein and virus crystals in solution by Mach-Zehnder interferometry.

To establish the importance of, and quantitatively evaluate, the macromolecular concentration gradients in the neighborhood of growing protein, virus, and nucleic acid crystals, a convenient, accurate, and nonintrusive method has been devised. This approach should prove particularly relevant in the rigorous comparison of crystals grown in a conventional laboratory setting with those grown in a microgravity environment. The method is based on precise determination of the local refractive index using Mach-Zehnder interferometry. Presented here are data for five protein and three virus systems. From data for these and other systems, optical monitoring experiments to measure local growth conditions and growth kinetics in liquid-liquid diffusion, batch, and vapor diffusion crystal growth experiments can be designed.

Interferometry↗
PubMed1995

Polymeric precipitants for the crystallization of macromolecules.

Nine different water soluble polymers reported to strongly affect the properties and structure of water were evaluated for their use in crystallizing a series of 24 different proteins, viruses, and conventional small molecules. All of the polymers produced crystals of some of the molecules and viruses tested, and of the 24 molecules tested, 14 were crystallized. In a number of cases, crystals of the molecules and viruses were obtained under very different conditions than were ever previously used. Because the selection of polymers employed here represents only a sampling of those available to experimenters, we conclude that the potential range of such polymers useful in macromolecular and small molecule crystallization may be very broad.

Animals↗
PubMed1995

Preliminary X-ray diffraction analysis of crystals of turnip yellow mosaic virus (TYMV).

Turnip yellow mosaic virus (TYMV) was purified from Chinese cabbage and crystallized in a form that permits high resolution structural analysis using X-ray diffraction. The crystals have a hexagonal bipyramidal morphology and often achieve dimensions of 1.0 x 1.0 x 0.5 mm. The crystals appear to be of hexagonal space group P6(2)22 with a=b=525 A, c=315 A, but we cannot strictly rule out the possibility that the space group is P622. They appear different than any crystals of TYMV previously reported. There are three T = 3 virus particles in the unit cell, which implies that one quarter of the particle, or 45 protein subunits, comprises the asymmetric unit of the crystal. Native data have been collected using synchrotron radiation to a resolution of 3.2 A.

Algorithms↗
PubMed1995

Preliminary X-ray diffraction analysis of crystals of tomato aspermy virus (TAV).

Tomato aspermy virus (TAV) is a member of the T = 3 cucumovirus group, and the chrysanthemum strain (C-TAV) has been crystallized in a form suitable for X-ray structural analysis. The crystals, which grow in 14-17% ethanol at pH 8.5, are of orthorhombic space group I222 with unit cell dimensions of a = 295.1 A, b = 320.5 A, and c = 383.6 A. There are two T = 3 virus particles in the unit cell, which means that they must be centered at 0,0,0 and 1/2, 1/2, 1/2 with icosahedral 222 symmetry elements coincident with crystallographic symmetry operators. The asymmetric unit of the crystals, therefore, contains one quarter of a virus particle, or 45 capsid subunits. Native diffraction data to 4 A resolution have been collected using synchrotron radiation, though data appear to be present beyond that resolution.

Crystallization↗
PubMed1995

Crystallization of intact monoclonal antibodies.

Attempts were made to crystallize four monoclonal antibodies, one IgG2a kappa and three IgG1 kappa. Using a PEG 3350 screen combined with detergents, and developed from our experiments with an IgG2a kappa antibody specific for canine lymphoma cells, crystals have now been obtained of two of these four immunoglobulins, an antiphenytoin and an antiphenobarbital antibody. A complex between the antiphenobarbital antibody and its drug antigen crystallized as well. The antibody for phenytoin has, to this point, produced only clustered microcrystals, marginally suitable for X-ray analysis. Single crystals of the IgG1 kappa antibody against phenobarbital, however, were characterized by X-ray diffraction to be primitive monoclinic, with unit cell dimensions a = 67 A, b = 193 A, c = 74 A, and beta = 110 degrees. These crystals have an entire IgG1 kappa molecule as the asymmetric unit and they diffract to at least 3.2 A resolution.

Animals↗
PubMed1995

Protein and virus crystal growth on international microgravity laboratory-2.

Two T = 1 and one T = 3 plant viruses, along with a protein, were crystallized in microgravity during the International Microgravity Laboratory-2 (IML-2) mission in July of 1994. The method used was liquid-liquid diffusion in the European Space Agency's Advanced Protein Crystallization Facility (APCF). Distinctive alterations in the habits of Turnip Yellow Mosaic Virus (TYMV) crystals and hexagonal canavalin crystals were observed. Crystals of cubic Satellite Tobacco Mosaic Virus (STMV) more than 30 times the volume of crystals grown in the laboratory were produced in microgravity. X-ray diffraction analysis demonstrated that both crystal forms of canavalin and the cubic STMV crystals diffracted to significantly higher resolution and had superior diffraction properties as judged by relative Wilson plots. It is postulated that the establishment of quasi-stable depletion zones around crystals growing in microgravity are responsible for self-regulated and more ordered growth.

Crystallization↗
PubMed1995

The structure of satellite panicum mosaic virus at 1.9 A resolution.

The crystal structure of satellite panicum mosaic virus (SPMV) has been solved by multiple isomorphous replacement and molecular replacement and refined at 1.9 A resolution. SPMV, a T = 1 icosahedral virus, is the smallest virus structure determined. The coat protein is an eight-stranded 'jelly roll' beta-barrel with an amino-terminal strand that extends into the interior of the virus, presumably interacting with the RNA. Regions of electron density on the interior of the protein capsid may be RNA, although it is not possible to construct any detailed model of the nucleic acid. Basic amino acid residues in contact with the nucleic acid show a considerable degree of disorder. The carboxy-terminal strand of the virus coat protein interacts with adjacent subunits, forming an additional beta-strand.

Amino Acid Sequence↗
PubMed1995

Mechanisms of growth for protein and virus crystals.

The growth of six protein and virus crystals was investigated in situ using atomic force microscopy. Most of the crystals grew principally on steps generated by two-dimensional nucleation on surfaces though some grew by development of spiral dislocations. Apoferritin grew by a rarely encountered mechanism, normal growth, usually associated only with melt or vapour phase crystallization. Cubic crystals of satellite tobacco mosaic virus (STMV) grew, at moderate to high levels of supersaturation, by the direct addition of three-dimensional nuclei followed by their rapid normal growth and lateral expansion, a mechanism not previously described to promote controlled and reproducible crystal growth from solutions. Biological macromolecules apparently utilize a more diverse range of growth mechanisms in their crystallization than any previously studied materials.

Apoferritins↗