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Biomedical subjects

M Chow

Publications and source records attributed to M Chow.

At least 73 records · Page 4Linked to original sources
PubMed1992

Folding and processing of the capsid protein precursor P1 is kinetically retarded in neutralization site 3B mutants of poliovirus.

Poliovirus mutants in neutralizing antigenic site 3B were constructed by replacing the glutamic acid residue at amino acid 74 of capsid protein VP2 (VP2074E), using site-specific mutagenesis methods. All viable mutants display small-plaque phenotypes. Characterization of these mutants indicates that capsid assembly is perturbed. Although the defect in capsid assembly reduces the yield of mutant virus particles per cell, the resultant assembled particle is wild-type-like in structure and infectivity. Analyses of capsid assembly intermediates show a transient accumulation of the unprocessed capsid protein precursor, P1, indicating that cleavage of the mutant P1 by the 3CD protease is retarded. The mutant VP0-VP3-VP1 complex generated upon P1 cleavage appears assembly competent, forming pentamer and empty capsid assembly intermediates and infectious virion particles. Although the structure of the infectious mutant virus is virtually identical with that of the wild-type virus, the thermal stability of the mutant virus is dramatically increased over that of the wild-type virus. Thus, mutations at this residue are pleiotropic, altering the kinetics of capsid assembly and generating a virus that is more thermostable and more resistant to neutralization by the site 3B monoclonal antibodies.

Amino Acid Sequence↗
PubMed1992

Identification of T-helper epitopes in the VP1 capsid protein of poliovirus.

Poliovirus-specific T lymphocytes were isolated from virus-immunized mice of different H-2 haplotypes. Immunological characterization of this population indicates that the effector population involved in the observed poliovirus-specific proliferative response was that of CD4-positive T-helper cells. Proliferative responses also were induced within these T-lymphocyte populations upon stimulation with either purified VP1 capsid protein or VP1 synthetic peptides. By using these synthetic peptides, several T-helper epitopes were identified. Generally, proliferative responses were observed in three regions of VP1. Two regions spanning VP1 residues 86 to 120 and 201 to 241 were recognized by T lymphocytes from BALB/c (H-2d), C57BL/6 (H-2b), and C3H/HeJ (H-2k) backgrounds. Analyses using synthetic peptides of nonoverlapping sequences indicated that the region spanning residues 201 to 241 may contain several T epitopes and may account for the strong proliferative response observed. In addition, for two of the three haplotypes examined, T epitopes were observed within residues 7 to 24 of VP1. Additional epitopes which appeared to be restricted to specific H-2 backgrounds were identified. T epitopes within VP1 that are common between different strains of mice appeared to lie within previously identified neutralizing antigenic sites in poliovirus.

Amino Acid Sequence↗
PubMed1991

The pharmacokinetics of, and humoral responses to, antigen delivered by microencapsulated liposomes.

The feasibility of creating a s.c. depot for sustained protein delivery with the goal of enhancing antigen immunogenicity was investigated. The depot was designed as antigen-laden liposomes of hydrogenated egg phosphatidylcholine and cholesterol (1:1 molar ratio) encapsulated in alginate-poly(L-lysine) microcapsules and evaluated using iodinated bovine serum albumin (BSA) as a model antigen. The in vivo release behavior of the liposomes and microencapsulated liposomes (MELs) was evaluated from the BSA serum concentration profiles after s.c. injection into rats and the pharmacokinetic parameters of 125I-labeled BSA appearance after s.c. or i.v. injections of BSA in saline. Maximal BSA concentrations were detected 11 h after s.c. injection in all rats. The BSA serum concentrations decreased rapidly in rats injected with BSA in saline or Freund's adjuvant and less rapidly in rats injected with BSA in liposomes or MELs. Four to 5 weeks after injection, BSA-associated radioactivity was detected only in sera of rats injected with BSA in liposomes or MELs. Fifty days after injection, 50% of the originally injected BSA was recovered form the s.c. sites of rats injected with BSA in MELs; no radioactivity was recovered from the other three groups of rats. The antigen-reactive antibody levels induced in rats immunized with BSA in MELs were 2- to 3-fold higher than those obtained in rats immunized with BSA in liposomes, saline, or Freund's adjuvant. More significantly, high antibody levels were maintained for more than 150 days after a single injection of BSA in MELs, suggesting that MELs can serve as a long-term single-dose immunization vehicle.

Animals↗
PubMed1991

Lipid-alginate interactions render changes in phospholipid bilayer permeability.

Lipid vesicles, e.g. liposomes, generally release their contents in a continuous manner. However, when these vesicles are entrapped in Ca-alginate and coated with poly(L-lysine), they release their contents in an unusual fashion, in 'bursts'. Molecular-level studies indicated that lipid-alginate interactions are responsible for changes in the barrier properties of lipid vesicles. Differential scanning calorimetry revealed that exposure of liposomes to alginate resulted in a 4-fold reduction in the phase transition enthalpy, with no change in the melting temperature. Size-exclusion chromatography of liposomes-in-alginate gave an additional liposomal peak with a smaller elution volume. These studies suggested that alginate is inserted into the lipid bilayer of vesicles. Lipid-alginate interactions were highly dependent on phospholipid head group charge and the phase transition temperature of the phospholipid. Based on these interactions, a mechanism to explain the 'burst' from these entrapped liposomes is suggested.

Alginates↗
PubMed1991

Identification of residues in VP2 that contribute to poliovirus neutralization antigenic site 3B.

Amino acid substitutions were placed at residues 74, 243, and 246 in capsid protein VP2 of poliovirus serotype 1, using site-specific mutagenesis methods. The proximity of these residues to those previously identified in neutralization site 3B suggests that these residues may also contribute to neutralization site 3B and potentially be under antibody selective pressure to mutate. However, sequence analyses of independent serotype 1 isolates indicate high sequence conservation at these residues, suggesting selective pressures are present within the virus to maintain sequences within these loop regions. All viable mutants display partial or complete resistance to neutralization by the site 3B neutralizing monoclonal antibodies. Cross-neutralization data with the site-specifically generated viral mutants confirm that these residues do indeed contribute to forming neutralization site 3B and also identify the participation of a new loop region within site 3B. However, many amino acid substitutions generate nonviable virus mutants and even conservative amino acid substitutions produce growth-compromised virus mutants. These data suggest that previous definition of neutralization antigenic sites by isolation of neutralization resistant mutants favors detection of viable mutant viruses with more normal growth characteristics and is inherently biased against detection of neutralization antigenic sites formed by residues critical for other stages of virus replication.

Amino Acid Sequence↗
PubMed1991

Myristoylation is important at multiple stages in poliovirus assembly.

The N-terminal glycine of the VP4 capsid subunit of poliovirus is covalently modified with myristic acid (C14 saturated fatty acid). To investigate the function of VP4 myristoylation in poliovirus replication, amino acid substitutions were placed within the myristoylation consensus sequence at the alanine residue (4003A) adjacent to the N-terminal glycine by using site-directed mutagenesis methods. Mutants which replace the alanine residue with a small hydrophobic residue such as leucine, valine, or glycine displayed normal levels of myristoylation and normal growth kinetics. Replacement with the polar amino acid histidine (4003A.H) also resulted in a level of myristoylation comparable to that of the wild type. However, replacement of the alanine residue with aspartic acid (4003A.D) caused a dramatic reduction (about 40 to 60%) in myristoylation levels of the VP4 precursors (P1 and VP0). In contrast, no differences in modification levels were found in either VP0 and VP4 proteins isolated from mature mutant virions, indicating that myristoylation is required for assembly of the infectious virion. The myristoylation levels of the VP0 proteins found in capsid assembly intermediates indicate that there is a strong but not absolute preference for myristoyl-modified subunits during pentamer formation. Complete myristoylation was observed in mature virions but not in assembly intermediates, indicating that there is a selection for myristoyl-modified subunits during stable RNA encapsidation to form the mature virus particle. In addition, even though mutant infectious virions are fully modified, the severe reduction in specific infectivity of both 4003A.D and 4003A.H purified viruses indicates that the amino acid residue adjacent to the N-terminal glycine apparently has an additional role early during viral infection and that mutations at this position induce pleiotropic effects.

Amino Acid Sequence↗
PubMed1990

Developing staff into clinical practitioners.

Developing clinical skills in pharmacy staff is a process that can enhance the services of a pharmacy department and improve the professional development and interest of the staff. Staff should be included in the development of a clinical philosophy and a training and ongoing development program that will achieve the desired goals should be planned. An MBO process may help to track the individual pharmacist's progress. Knowledgeable, motivated staff are the key ingredient in achieving success in providing pharmacy services.

Clinical Competence↗
PubMed1989

Stabilization of poliovirus against heat inactivation.

Fatty acids and related compounds, as well as many salts, stabilize poliovirus against heat inactivation. Addition of myristate to poliovirus prevents heat-induced conformational changes which are detected by trypsin degradation of the virion. Using equilibrium dialysis, we found that several molecules of myristate bind per virion. The relative stabilizing potencies of the salts can be explained by the Hofmeister effect.

Fatty Acids, Nonesterified↗
PubMed1989

Structural factors that control conformational transitions and serotype specificity in type 3 poliovirus.

The three-dimensional structure of the Sabin strain of type 3 poliovirus has been determined at 2.4 A resolution. Significant structural differences with the Mahoney strain of type 1 poliovirus are confined to loops and terminal extensions of the capsid proteins, occur in all of the major antigenic sites of the virion and typically involve insertions, deletions or the replacement of prolines. Several newly identified components of the structure participate in assembly-dependent interactions which are relevant to the biologically important processes of viral assembly and uncoating. These include two sites of lipid substitution, two putative nucleotides and a beta sheet formed by the N-termini of capsid proteins VP4 and VP1. The structure provides an explanation for the temperature sensitive phenotype of the P3/Sabin strain. Amino acids that regulate temperature sensitivity in type 3 poliovirus are located in the interfaces between promoters, in the binding site for a lipid substituent and in an assembly-dependent extended beta sheet that stabilizes the association of pentamers. Several lines of evidence indicate that these structural components also control conformational transitions at various stages of the viral life cycle.

Antigens, Viral↗
PubMed1989

SPARC: a Ca2+-binding extracellular protein associated with endothelial cell injury and proliferation.

SPARC (Secreted Protein that is Acidic and Rich in Cysteine) is a Ca2+-binding, stress-related protein released in vitro by both malignant and normal cells derived from all primordial germ layers. It is specifically elevated in endothelial cells as a result of "culture shock" (characterized by high levels of proliferation and migration) and exhibits density-dependent secretion. Exposure of bovine aortic endothelial cells to endotoxin results in a 70-100% increase in secreted protein, with a three-fold increase in SPARC. Immunofluorescence histochemistry on mouse tissues revealed (a) a preferential association of SPARC with highly proliferative cells (e.g., gut epithelia, mammary gland, and epidermis), (b) a cell surface or stromal location in thymus, lung, and salivary gland, (c) staining of epididymidal epithelium and testicular cells, and (d) an association with somites of 14 d mouse embryos. We envision SPARC as an extracellular modulator of Ca2+ and other cation-sensitive proteins/proteinases, that facilitates cellular proliferation in response to injury and to developmental signals.

Animals↗
PubMed1989

Characterization of elastin protein and mRNA from salmonid fish (Oncorhynchus kisutch).

1. Elastin was isolated from the bulbus arteriosus of a salmonid fish. Monoclonal and polyclonal antibodies, elicited against a CNBr digest of this protein, immunoprecipitated a polypeptide of Mr 43,000 from fish cell culture medium. 2. Cell-free translation of salmon poly A+ RNA produced a protein of approximately 43 kD that was immunoprecipitated with anti-elastin antibodies. The corresponding mRNA had an approximate Mr of 2 kb. 3. Despite similarities in amino acid composition, the differences in Mr between mammalian and salmon mRNA and protein suggest a divergence of fish and higher vertebrate elastins from an earlier ancestral gene.

Amino Acids↗
PubMed1988

Trypsin hydrolysis of X-phenyl hippurates.

The kinetics of hydrolysis of eight substituted phenyl hippurates by trypsin at pH values 6, 7 and 8 were investigated and the kinetic constants Km, kcat (kcatalysis) and kcat/Km were shown to fit the Hammett equation. The rho (rho) value obtained from the correlation of trypsin binding with this class of esters was compared with that obtained with other serine and cysteine proteases. The rho value for trypsin was similar to that obtained for alpha-chymotrypsin in that both enzymes reveal a pronounced dependence on through resonance (sigma-) in the formation of the Michaelis complex and the acyl-enzyme. It is apparent that through resonance facilitates the leaving of the phenoxy moiety during catalysis in the serine proteases but not in the case of the cysteine or bacterial serine proteases.

Binding Sites↗
PubMed1988

Benefits expected from simple conformal radiotherapy in the treatment of pelvic tumours.

In 20 patients with invasive bladder cancer suitable for radical radiotherapy, a simple conformal planning technique has been compared with conventional beam arrangements in terms of normal tissue sparing. The median treatment volume for the group was reduced from 2275 to 1416 cm3 by the introduction of conformal planning. More specifically, in 13/20 patients (65%) the percentage volume of rectum irradiated to 90% of the isocentric dose was reduced by more than 30%, although the extent of rectal sparing varied greatly between patients. Overall, conformal planning appeared to be less successful at reducing the volume of large and small bowel irradiated to high dose. However, the data suggest that considerable benefit can be expected for those patients most at risk of morbidity by virtue of high bowel volumes included within the treatment length. A randomised trial is now being set up to determine the clinical impact of this planning technique in terms of reduced bowel morbidity.

Humans↗
PubMed1988

Three-dimensional structure of poliovirus serotype 1 neutralizing determinants.

Antigenic mutants of poliovirus (Sabin strain, serotype 1) were isolated by the resistance of the virus to anti-Sabin neutralizing monoclonal antibodies. The amino acid replacements within the capsid protein sequence causing the altered antigenicity were identified for each of 63 isolates. The mutations cluster into distinct nonoverlapping peptide segments that group into three general immunological phenotypes on the basis of cross-neutralization analyses with 15 neutralizing anti-Sabin monoclonal antibodies. Location of the mutated amino acid residues within the three-dimensional structure of the virion indicates that the majority of these amino acid residues are highly exposed and located within prominent structural features of the viral surface. Those mutated amino acid residues that are less accessible to antibody interaction are often involved in hydrogen bonds or salt bridges that would stabilize the local tertiary structure of the antigenic site. The interactions of the peptide segments that form these neutralizing sites suggest specific models for the generation of neutralization-resistant variants and for the interaction between the viral surface and antibody.

Antibodies, Monoclonal↗
PubMed1986

High-altitude pulmonary edema. Characteristics of lung lavage fluid.

To evaluate the cellular and biochemical composition of bronchoalveolar fluid in high-altitude pulmonary edema (HAPE), we performed bronchoalveolar lavage in three climbers with HAPE in a research facility at 4400 m on Mount McKinley. Three healthy climbers were used as controls. The HAPE fluids contained marked increases in high-molecular-weight proteins, erythrocytes, and leukocytes, most of which were alveolar macrophages. The HAPE fluids also contained detectable amounts of leukotriene B4 and other lipoxygenase products of arachidonic acid metabolism, complement fragments (C5a), inhibitors of neutrophil chemotaxis, and acid proteases but not hydroxyproline, a constituent of collagen. The data from this study indicate that HAPE involves a transient "large pore" leak in the pulmonary circulation. Despite the presence of two potent mediators of inflammation, leukotriene B4 and C5a, HAPE is not characterized by the intense neutrophil accumulation that is typical of other forms of acute lung injury.

Adult↗
PubMed1986

A new symmetry: A anti-B is anti-(B anti-A), and reverse enhancement.

Immune system network theory leads to a new symmetry, namely that the antibodies produced in an allogeneic A anti-B immune response (where A and B are, say, two different mouse strains), should have complementary shapes to the antibodies in a B anti-A response. That is, A anti-B is anti-(B anti-A). This symmetry is due to the existence of two readily separable populations of antibodies that are present in alloantisera: anti-foreign and anti-anti-self antibodies. The theoretical basis for the symmetry is described, and results indicating the presence of anti-anti-self antibodies in each of 12 alloantisera (six made in B10-congenic strains, and six made with the unrelated chains CBA, SJL, and C57BL/6) are reported. The finding that hyperimmune alloantisera routinely contain anti-anti-self antibodies suggests that network regulation plays an important role in maintaining self-tolerance during responses to allogeneic cells. We further show that A anti-B serum absorbed against B can specifically prolong the survival of A grafts in a B strain animal. We suggest that this result can be interpreted as being due to A anti-(B anti-A) antibodies preventing B anti-A cells from rejecting the A grafts. We call this phenomenon "reverse enhancement" because it involves the converse antiserum to that used in conventional enhancement of graft survival by specific antibodies.

Animals↗
PubMed1986

Identification and characterization of a protein covalently bound to DNA of minute virus of mice.

We identified a protein which is covalently linked to a fraction of the DNA synthesized in cells infected with minute virus of mice. This protein is specifically bound to the 5' terminus of the extended terminal conformers of the minute virus of mice replicative-form DNA species and of a variable fraction of single-stranded viral DNA. The chemical stability of the protein-DNA linkage is characteristic of a phosphodiester bond between a tyrosine residue in the protein and the 5' end of the DNA. The terminal protein (TP) bound on all DNA forms has a relative molecular weight of 60,000; it is also seen free in extracts from infected cells. Immunologic comparison of the TP with the other known viral proteins suggests that the TP is not related to the capsid proteins or NS-1.

Animals↗