Structural determination of the capsular polysaccharide antigen of type II group B Streptococcus.

Abstract

I5The native polysaccharide antigen isolated from type I1 group B Streptococcus contains Dgalactose, D-glucose, 2-acetamido-2-deoxy-~-glucose, and sialic acid in the molar ratio of 3:2:1:1.The application of methylation and nmr spectroscopic analyses to the native type 11 antigen and some of its specifically degraded products enabled the structure of the native type I1 antigen to be elucidated.The native type I1 antigen is composed of the following repeating unit PD-Galp (1 + 4) PD-GIC~ (1 + 3) BD-GIC~ (1 + 2) PDGalp (1--4) b -G l c p N A c ( l + 3) 6 3 t T 1 2 PD-Galp aD-NeupNAc Unlike the native types Ia, Ib, and I11 group B streptococcal polysaccharides, the native type I1 antigen contains terminal 8-D-galactopyranosyl residues in addition to terminal sialic acid residues.The terminal sialic acid residues of the native type I1 antigen are also unique among those of the other group B streptococcal antigens in that they are not neuraminidase-sensitive and are attached directly to the backbone of the type I1 antigen.