Streptococcus pneumoniae capsular polysaccharide serotype 19F (19F CPS)

The Streptococcus pneumoniae capsular polysaccharide serotype 19F (19F CPS) is a dominant surface structure composed of repeating trisaccharide units of N-acetyl-D-mannosamine (ManNAc) β-(1→4) linked to D-glucose (Glc), which is then α-(1→2) linked to L-rhamnose (Rha), connected via α-(1→4) phosphodiester bridges, and covalently attached to cell wall peptidoglycan via a 1,6 glycosidic bond between Glc and GlcNAc. This capsule is a key virulence factor that evades host immunity by inhibiting opsonophagocytosis, complement activation, and immunoglobulin binding, enabling bacterial survival in nasal mucus, epithelial attachment, and systemic infection. Serotype 19F is a prevalent cause of invasive pneumococcal disease, especially in young children, and is included in vaccines like PCV13 and PPV23 due to its antigenicity, though protection is strictly serotype-specific with limited cross-reactivity to 19A despite structural similarities. Biosynthesis involves the cps19f locus, encoding serotype-specific glycosyltransferases, flippase Wzx, polymerase Wzy, and precursor synthesis enzymes, allowing precise repeat unit assembly. Challenges include capsule switching through large DNA recombination events, contributing to antimicrobial resistance and vaccine evasion in clinical isolates.

Other names

Streptococcus pneumoniae 19F capsular polysaccharideSp 19F CPSType 19F polysaccharide

Induction of serotype-specific antibodies for opsonophagocytic killing. Targeting of phosphorylated disaccharide epitope (ManNAc-β-(1→4)-Glc) for antibody recognition.