Substrate specificity of two bacteriophage-associated endo-N-acetylneuraminidases

Abstract

For Escherichia coli Bos12 (O16:K92:H-), a bacteriophage (phi 92) has been isolated which carries a depolymerase active on the K92 capsular polysaccharide. As seen under the electron microscope, phi 92 belongs to Bradley's morphology group A and is different from the phage phi 1.2 previously described (Kwiatkowski et al., J. Virol. 43:697-704, 1982), which grows on E. coli K235 (O1:K1:H-), depolymerizes colominic acid, and belongs to morphology group C. The specificity of the phi 1.2- and phi 92-associated endo-N-acetylneuraminidases has been studied with respect to the following substrates (all alkali treated, and where NeuNAc represents N-acetylneuraminic acid): (i) [-alpha-NeuNAc-(2 leads to 8)-]n (colominic acid), (ii) [-alpha-NeuNAc-(2 leads to 8)-alpha-NeuNAc-(2 leads to 9)-]n (E. coli K92 polysaccharide), and (iii) [-alpha-NeuNAc-(2 leads to 9)-]n (Neisseria meningitidis type C capsular polysaccharide). The increase in periodate consumption of these glycans upon incubation with purified phi 1.2 or phi 92 particles was measured, and the split products obtained from all substrates after exhaustive degradation were analyzed by gel chromatography. It was found that the Neisseria polysaccharide is not appreciably affected by either virus enzyme and that phi 1.2 only depolymerizes a small fraction of the K92 glycan. Colominic acid, however, is completely degraded by both agents, phi 92 yielding smaller fragments (one to six NeuNAc residues) than phi 1.2 (two to seven). Phage phi 92 additionally depolymerizes the K92 glycan, essentially to oligosaccharides of two, four, and six residues. The size distribution of these K92 oligosaccharides indicates that the phi 92 enzyme predominantly cleaves the alpha(2 leads to 8) linkages in this polymer.