Streptococcus pneumoniae capsular polysaccharide serotype 5 (CPS5)

The Streptococcus pneumoniae capsular polysaccharide serotype 5 (CPS5) is a high-molecular-weight polymer of repeating oligosaccharide units that forms the outermost layer of the bacterial cell wall, enabling immune evasion by inhibiting phagocytosis and complement activation. Encoded by the serotype-specific *cps* locus, CPS5 biosynthesis involves conserved genes like *cpsABCD* for regulation and polymerization, plus serotype-unique glycosyltransferases for its distinct structure, typically featuring branched or linear monosaccharide chains with possible O-acetylation. This capsule is critical for virulence in invasive pneumococcal diseases such as pneumonia, meningitis, and sepsis, with serotype 5 contributing to global disease burden despite vaccine inclusion. Vaccines target CPS5 by conjugating it to carrier proteins (e.g., diphtheria CRM197), eliciting high-affinity IgG antibodies that promote bacterial clearance via opsonization. Targeting CPS5 reduces invasive disease incidence but faces challenges like antigenic variability across >100 serotypes and emergence of non-vaccine types.

Other names

S. pneumoniae type 5 capsular polysaccharidepneumococcal capsular polysaccharide serotype 5serotype 5 CPS

Induces serotype-specific antibody production via conjugation to carrier proteins like CRM197 or tetanus toxoid, promoting T-cell dependent immune response and opsonophagocytic killing of encapsulated bacteria