Biomedical subjects

M R Lifely

Publications and source records attributed to M R Lifely.

22 records · Page 2Linked to original sources

PubMed1984

Rate, mechanism, and immunochemical studies of lactonisation in serogroup B and C polysaccharides of Neisseria meningitidis.

Meningococcal Serogroup B polysaccharide and colominic acid, which are (2----8)-alpha-linked homopolymers of sialic acid, undergo lactonisation at low pH at a rate which is dependent upon the molecular size and upon the salt form (Na+ or Ca2+). Meningococcal Serogroup C polysaccharide, a (2----9)-alpha-linked homopolymer of sialic acid with acetyl groups present at O-7 and/or O-8, reacts with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide to give an O-acylisourea. The rate of formation of O-acylisourea does not differ substantially between O-acetylated (O-Ac+) C, non-O-acetylated (O-Ac-) C, and B polysaccharide. 13C-N.m.r. spectroscopy shows that, in the absence of O-acetyl groups, the majority of the activated carboxyl groups of C polysaccharide condense with an adjacent HO-8 to form a delta-lactone. Immunochemical studies show that the antigenicity of B polysaccharide is markedly reduced on lactonisation of less than 20%, as measured by a radioimmunoassay using an anti-B monoclonal antibody, and that low-molecular-weight colominic acid is poorly antigenic both before and after lactonisation, suggesting the presence of conformational determinants on B polysaccharide. In contrast, lactonisation and/or formation of O-acylisourea groups in the (O-Ac+)-C polysaccharide does not cause a significant decrease in the antigenicity, which is consistent with a sequential (structural) determinant on the molecule.

Hydrogen-Ion Concentration↗

PubMed1984

Conformational and dynamic differences between N. meningitidis serogroup B and C polysaccharides, using n.m.r. spectroscopy and molecular mechanics calculations.

1H-N.m.r. spectroscopy has been used to determine the conformation in aqueous solution of the sialic acid residues of the N. meningitidis serogroup B and non-O-acetylated (O-Ac-)-C polysaccharides, and of N-acetylneuraminic acid (NeuNAc). In all cases, the sugar adopts the 2C5 conformation. The side-chain of NeuNAc adopts a conformation such that H-7 and H-8 are approximately anti-periplanar. This conformation is also found in the (O-Ac-)-C polysaccharide, whereas H-7 and H-8 are gauche in the B polysaccharide. Molecular mechanics calculations have been used to probe the conformational preferences of the variously linked sialic acid residues, and the results are in general agreement with those based on the 1H-n.m.r. data. The 13C-n.m.r. spin-lattice relaxation-times have been interpreted in terms of the molecular dynamics of the B and (O-Ac-)-C polysaccharides. Molecular correlation times have been calculated and details of internal rotational or segmental motion elucidated. The C polysaccharide is characterised by internal or segmental motion in the C-7 to C-9 side-chain of the sialic acid repeating-unit, whereas the B polysaccharide has little or no such movement and tumbles in solution as a rigid species with internal rotation of only the pendant C-9 group. The conformational differences suggest a substantially different three-dimensional structure in solution for these polysaccharides.

Magnetic Resonance Spectroscopy↗

PubMed1981

Sialic acid polysaccharide antigens of Neisseria meningitidis and Escherichia coli: esterification between adjacent residues.

Colominic acid and meningococcal Group B polysaccharide, both (2 leads to 8)-alpha-linked homopolymers of sialic acid, are made water-insoluble either by reaction with a carbodiimide in aqueous solution at pH 4.75 or by treatment with 48% aqueous hydrofluoric acid at 0 degrees for 48 h. I.r. spectra of the products show a major band near 1750 cm-1, consistent with ester formation; this band virtually disappears after mild, alkali treatment. Esterification also occurs by incubating the native polysaccharides below pH 6.0, and their i.r. spectra show that the degree of esterification increases as the pH is lowered. The relatively low molecular weight of these partially esterified, water-soluble polymers is consistent with intra- rather than inter-molecular ester formation. Counter-current immunoelectrophoresis shows that esterification of approximately 9% is sufficient to abolish immunoprecipitation. 13C-N.m.r. spectroscopy of fully esterified colominic acid provides strong evidence for cross-linking between the carboxyl group of one residue and HO-9 of an adjoining residue. Meningococcal serogroup C polysaccharide, a (2 leads to 9)-alpha-linked homopolymer of sialic acid containing O-acetyl groups at C-7 and/or C-8, does not undergo intramolecular esterification after carbodiimide treatment. However, upon O-deacetylation of the polysaccharide, esterification occurs.

Escherichia coli↗

PubMed1980

The teichuronic acid from the walls of Bacillus licheniformis A.T.C.C. 9945.

The teichuronic acid of Bacillus licheniformis A.T.C.C. 9945 grown under phosphate limitation was isolated from the cell walls and purified by ion-exchange and Sephadex chromatography. The detailed structure of the polysaccharide was established by methylation analysis, periodate oxidation and partial acid hydrolysis. The polymer is composed of tetrasaccharide repeating units with the structure [GlcA beta(1 leads to 4)GlcA beta(1 leads to 3)GalNAc beta(1 leads to 6)GalNAc alpha(1 leads to 4)n. 13C n.m.r. analysis has confirmed most of the structural features of the polysaccharide and, in particular, the anomeric configurations and linkage positions of substituents. The teichuronic acid from glucose-limited cells was identical with that from cells grown under phosphate limitation.

Bacillus↗