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

• Published in: Journal of biochemistry (Tokyo) Vol. 131; no. 2; pp. 183 - 191
• Main Authors: Watanabe, Masaki, Miyake, Katsuhide, Yanae, Kouji, Kataoka, Yohei, Koizumi, Satoshi, Endo, Tetsuo, Ozaki, Akio, Iijima, Shinji
• Format: Journal Article
• Language: English
• Published: 01.02.2002
• ISSN: 0021-924X
• DOI: 10.1093/oxfordjournals.jbchem.a003086

A group B streptococcus, Streptococcus agalactiae type Ib, produces a high-molecular-weight polysaccharide consisting of the following pentasaccharide repeating unit: -> 4)-[ alpha -D-NeupNAc-(2 -> 3)- beta -D-Galp-(1 -> 3)- beta -D-GlcpNAc-(1 -> 3)]- beta -D-Galp-(1 -> 4)- beta -D-Glcp-(1 ->. 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 Ia, which has a similar but distinct CP, showed that the translation products of cpsla and cpslb genes exhibited very high homology except for those of cpsJ and K. In the type Ia strain, cpslaJ encodes beta 1,4-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 beta 1,3-linkage to GlcNAc. The low homology between the type Ia and Ib CpsJs seems to reflect this difference. By enzymatic activity measurement, the cpslbJ product was found to display beta 1,3-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.