Primary health care and adolescence.
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Adolescent↗
Biomedical subjects
A McPherson
Publications and source records attributed to A McPherson.
The science of macromolecular crystallization.
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Crystallization↗
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↗
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↗
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↗
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↗
The three-dimensional structure of an intact monoclonal antibody for canine lymphoma.
Crystal structures of Fab antibody fragments determined by X-ray diffraction characteristically feature four-domain, beta-barrel arrangements. A human antibody Fc fragment has also been found to have four beta-barrel domains. The structures of a few intact antibodies have been solved: in two myeloma proteins, the flexible hinge regions that connect the Fc to the Fab segments were deleted so the molecules were non-functional, structurally restrained, T-shaped antibodies; a third antibody, Kol, had no hinge residues missing but the Fc region was sufficiently disordered that it was not possible to relate its disposition accurately with respect to the Fab components. Here we report the structure at 3.5 A resolution of an IgG2a antitumour monoclonal antibody which contains an intact hinge region and was solved in a triclinic crystal by molecular replacement using known Fc and Fab fragments. The antibody is asymmetric, reflecting its dynamic character. There are two local, apparently independent, dyads in the molecule. One relates the heavy chains in the Fc, the other relates the constant domains of the Fabs. The variable domains are not related by this 2-fold axis because of the different Fab elbow angles of 159 degrees and 143 degrees. The Fc has assumed an asymmetric, oblique orientation with respect to loosely tethered yet almost collinear Fabs. Our study enables the two antigen-binding segments as well as the Fc portion of a functional molecule to be visualized and illustrates the flexibility of these immune response proteins.
Animals↗
Crystal structure disposition of thymidylic acid tetramer in complex with ribonuclease A.
The crystal structure of ribonuclease A with bound thymidylic acid tetramer is reported at 2.5-A resolution. The diffusion of the tetramer into native orthorhombic crystals of the ribonuclease allows for the formation of a structurally stable complex where the single-stranded nucleic acid enters and leaves the enzyme's catalytic region in a persistent 5'-3' direction. The binding of the tetramer to the enzyme's surface is facilitated and mediated by electrostatic interactions between basic protein residues and nucleotide phosphates. Two pyrimidine nucleotides are bound to the enzyme's active site in a manner similar to that observed for other complexes between ribonuclease A and nucleic acid oligomers.
Animals↗
Crystallization and preliminary X-ray analysis of human endothelin.
Endothelin, a potent regulator of vasoconstriction and hypertension, is a naturally produced peptide of 21 amino acids containing two disulfide bonds. We have crystallized endothelin from humans using the vapor-diffusion technique, characterized the crystals by X-ray diffraction analysis, and have collected the X-ray intensities to a resolution of 1.8 A. The crystals, which demonstrate physical properties similar to most protein crystals and have a comparable solvent content, are hexagonal prisms that frequently grow to lengths of 400 microns and widths of 150 microns. The space group of the crystals is P6(1)22 (or P6(5)22), with a = 27.4, c = 79.6 A. There is one molecule of endothelin in the asymmetric unit of the crystals.
Crystallization↗
Preliminary crystallographic study of peanut peroxidase.
The cationic isozyme of peroxidase isolated from suspension cultures of peanut cells is a heme-containing and calcium-dependent glycoprotein having four covalently attached oligosaccharide chains. Attempts were made to crystallize the glycoprotein for X-ray diffraction analysis, and these have met with some success. Crystals have now been grown that are suitable for a full three-dimensional structural analysis. The crystals are thin plates and we have shown them to be of the orthorhombic space group P2(1)2(1)2(1) with a = 48.1, b = 97.2, c = 146.2 A. The crystals diffract to beyond 2.8 A resolution, appear to be stable to lengthy X-ray exposure, and contain two molecules of 40,000 daltons each in the asymmetric unit.
Arachis↗
Macromolecular crystal growth experiments on International Microgravity Laboratory--1.
Macromolecular crystal growth experiments, using satellite tobacco mosaic virus (STMV) and canavalin from jack beans as samples, were conducted on a US Space Shuttle mission designated International Microgravity Laboratory--1 (IML-1), flown January 22-29, 1992. Parallel experiments using identical samples were carried out in both a vapor diffusion-based device (PCG) and a liquid-liquid diffusion-based instrument (CRYOSTAT). The experiments in each device were run at 20-22 degrees C and at colder temperatures. Crystals were grown in virtually every trial, but the characteristics of the crystals were highly dependent on the crystallization technique employed and the temperature experience of the sample. In general, very good results, based on visual inspection of the crystals, were obtained in both PCG and CRYOSTAT. Unusually impressive results were, however, achieved for STMV in the CRYOSTAT instrument. STMV crystals grown in microgravity by liquid-liquid diffusion were more than 10-fold greater in total volume than any STMV crystals previously grown in the laboratory. X-ray diffraction data collected from eight STMV crystals grown in CRYOSTAT demonstrated a substantial improvement in diffraction quality over the entire resolution range when compared to data from crystals grown on Earth. In addition, the extent of the diffraction pattern for the STMV crystals grown in space extended to 1.8 A resolution, whereas the best crystals that were ever grown under conditions of Earth's gravity produced data limited to 2.3 A resolution. Other observations indicate that the growth of macromolecular crystals is indeed influenced by the presence or absence of gravity. These observations further suggest, consistent with earlier results, that the elimination of gravity provides a more favorable environment for such processes.
Crystallization↗
PCR cloning of the full-length cDNA for the seed protein canavalin from the jack bean plant, Canavalis ensiformis.
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Amino Acid Sequence↗
Characterization of crystals of an Fab fragment of a murine monoclonal antibody.
The Fab fragment of an antibody, made against an E2-specific feline infectious peritonitis virus neutralizing antibody, has been crystallized in a form suitable for X-ray diffraction analysis from PEG 4000 using vapor diffusion methods. The Fab fragment crystals diffract to about 2.9 A resolution and are of triclinic space group P1. Unit cell dimensions, by which the reciprocal lattice can be indexed, are a = 57.16 A, b = 70.85 A, c = 75.81 A, alpha = 85.11 degrees, beta = 121.28 degrees and gamma = 116.33 degrees. There are two Fab fragments comprising the asymmetric unit of the crystals. The presence of a pseudo-mirror plane in the diffraction pattern suggests the presence of at least an approximate dyad axis relating the two Fab fragments within the asymmetric unit.
Animals↗
Characterization of two crystal forms of cytochrome c from Valida membranaefaciens.
Two different crystal forms of cytochrome c from the yeast Valida membranaefaciens have been grown by vapor diffusion from polyethylene glycol 4000. Both have been characterized by X-ray diffraction. The first crystal form was grown at 277 K but proved unstable and dissolved when the temperature was increased above 288 K. This crystal was of triclinic space group P1 and had unit-cell dimensions of a = 68.4, b = 35.7, c = 33.24 A, alpha = 116.9, beta = 114.9, gamma = 75.0 degrees. Following dissolution of the triclinic crystals, the second crystal form also grew at 277 K but remained stable even at room temperature. It was of orthorhombic space group P2(1)2(1)2(1) with cell dimensions a = 27.95, b = 63.68, and c = 64.28 A. Although rather small in size, both crystal forms diffracted X-rays well and the resolution of the patterns extended beyond 3 A.
Crystallization↗
The Oregon plan: rationing in a rational society.
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Canada↗
Characterization of crystals of an intact monoclonal antibody for canine lymphoma.
A monoclonal antibody of the subclass IgG2a specific for canine lymphoma cells has been crystallized by vapor diffusion from polyethylene glycol 8000. the crystals, which occasionally measure nearly a millimeter on edge, have been examined by X-ray diffraction. The crystals are of triclinic space group P1 with unit cell parameters of a = 66.39 A, b = 77.34 A, c = 101.42 A, alpha = 87.60 degrees, beta = 92.55 degrees, gamma = 97.54 degrees and cell volume of V = 4.84 x 10(5) A3. There is one entire antibody molecule as the asymmetric unit of the crystals. Three-dimensional X-ray diffraction data have been collected to 2.8 A resolution and a self rotation function calculation shows a pronounced peak indicating at least an approximate non-crystallographic dyad axis.
Animals↗
Preliminary investigation of crystals of the neutral lipase from Pseudomonas fluorescens.
The neutral lipase from the bacteria Pseudomonas fluorescens, marketed under the trade name LpL-200S, has been crystallized in a form suitable for X-ray diffraction analysis from 35% n-propanol at pH 8.5. The crystals are monoclinic prisms and are of space group C2 with a = 91.00 A, b = 47.17 A, c = 35.21 A and beta = 121.43 degrees. There is one molecule of the protein as the asymmetric unit of the crystals. The diffraction pattern extends to at least 1.6 A resolution and the crystals are extremely robust in terms of X-ray exposure.
Crystallization↗
Antibody-directed drug discovery.
By harnessing the remarkable power of the immune system to access the three-dimensional chemical information sequestered in target sites for drug ligands, antibody-directed drug discovery speeds the design of new therapeutic entities.
Antibodies↗