Molecular Characterization of a Novel .BETA.1,3-Galactosyltransferase for Capsular Polysaccharide Synthesis by Streptococcus agalactiae Type Ib.

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Description

A group B streptococcus, Streptococcus agalactiae type Ib, produces a high-molecularweight polysaccharide consisting of the following pentasaccharide repeating unit: →4)-[γ-D-NeupNAc-(2→3)-β-D-Galp-(1→s3)-β-D-GlcpNAc-(1→3)]-→-D-Galp-(1→4)-→-D-Glcp-(l→. The type-specific capsular polysaccharide (CP) synthesis (cps) genes of this strain were cloned and analyzed. A cloned 10-kb DNA fragment contained cpslbE to L and neu (neuraminic acid synthesis gene) B. Comparison of the gene products with those of S. agalactiae type la, which has a similar but distinct CP, showed that the translation products of cpsIa and cpsIb genes exhibited very high homology except for those of cpsJ and K. In the type la strain, cpsIaJ encodes β1, 4-galactosyltransferase, which catalyzes the transfer of galactose as the fourth monosaccharide of the sugar repeating unit. In the type Ib CP, this galactose forms a β1, 3-linkage to GlcNAc. The low homology between the type la and Ib CpsJs seems to reflect this difference. By enzymatic activity measurement, the cpslbJ product was found to display β1, 3-galactosyltransferase activity. Furthermore, hydrophobic cluster analysis clarified the similarities and differences of the structures in N-terminal regions, including the DXD motif, between the galactosyltransferases.

Journal

  • J Biochem (Tokyo)

    J Biochem (Tokyo) 131 (2), 183-191, 2002

    The Japanese Biochemical Society

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