Group B Streptococcus capsular polysaccharide serotype Ia (GBS CPS Ia)

The Group B Streptococcus capsular polysaccharide serotype Ia is a surface polysaccharide of Streptococcus agalactiae (Group B Streptococcus, GBS) that defines one of nine capsular serotypes (Ia, Ib, II-VIII).[1][2][6] It consists of repeating units (PRUs) with a conserved disaccharide backbone of β-D-Glc-(1→4)-β-D-Gal and a variable trisaccharide side chain β-D-Gal-(1→4)-β-D-GlcNAc linked β-D-GlcNAc-(1→3) to the galactose of the disaccharide; PRUs are polymerized via β-D-Glc-(1→4)-β-D-Gal linkages.[1][2] The structure includes glucose, galactose, N-acetylglucosamine, and N-acetylneuraminic acid (sialic acid).[1][2] Biosynthesis is directed by the cps operon (e.g., cps1aG, cps1aH, cps1aI, cps1aJ, cps1aK), encoding glycosyltransferases with serotype-specific functions like Cps1aI (1→3 N-acetylglucosaminyltransferase) and Cps1aJ (β-D-galactosyltransferase); genetic diversity arises from horizontal gene transfer.[1][2] It confers antigenic specificity, aids immune evasion via antiphagocytic properties, and is structurally related to serotypes Ib, III, and VI, sharing motifs that balance variation and conservation for survival.[1][4] As a major virulence factor, it is a target for serotype-specific diagnostics, opsonophagocytic antibodies, and glycoconjugate vaccine development, though focused studies often highlight serotype III.[1][3][5]

Other names

Type Ia capsular polysaccharideGBS type Ia polysaccharideSerotype Ia CPS