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Streptococcus pneumoniae serotype 3 capsular polysaccharide (Pn3P)

Target: Pn3P
Molecular classification: Other (bacterial capsular polysaccharide)

Overview

The Streptococcus pneumoniae serotype 3 capsular polysaccharide (Pn3P) is a mucinous surface structure composed of repeating disaccharide units of glucose (Glc) and glucuronic acid (GlcA), synthesized by the cps3/cap3 locus encoding UDP-Glc dehydrogenase (cps3D/cap3A), type 3 synthase (cps3S/cap3B), and Glc-1-phosphate uridylyltransferase (cps3U/cap3C). It is the major virulence factor, shielding the bacterium from phagocytosis by inhibiting complement activation, limiting immunoglobulin and C-reactive protein binding, and reducing C3b/iC3b opsonization. Pn3P links directly to cell wall peptidoglycan via a 1,6 glycosidic bond from its reducing-end Glc to GlcNAc. Serotype 3 is highly virulent, prevalent in severe infections, and resistant to standard vaccines and antibiotics; therapeutic strategies target its degradation or elicit specific antibodies.

Other names: type 3 capsular polysaccharide (CPS)pneumococcal type 3 polysaccharidePPS3

Mechanism of action

Vaccine induces opsonic antibodies for phagocytosis and agglutination; Pn3Pase degrades CPS to expose bacteria to immune clearance and phagocytosis

Biological functions

Virulence factorinhibits complement pathwaysreduces opsonizationimpairs phagocytosisprotects against desiccationaids colonization

Disease associations

Infection (pneumococcal diseaseinvasive pneumococcal diseasecommunity-acquired pneumonia)

Safety considerations

Serotype 3 shows poor response to current vaccines (requires higher antibody titers)rising antibiotic resistancehigh CPS release interferes with antibody-mediated killing

Interacting drugs

PCV13 conjugate vaccine (targets Pn3P as component)

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