Streptococcus pneumoniae capsular polysaccharide serotype 3 (CPS3)

The Streptococcus pneumoniae capsular polysaccharide serotype 3 (CPS3) is a dominant surface structure composed of repeating disaccharide units of glucose and glucuronic acid, synthesized by a processive β-glycosyltransferase encoded by cps3S (also cap3B) in the cps3 locus, along with UDP-Glc dehydrogenase (cps3D) for substrate production.[1][3][6] This thicker, loosely attached capsule acts as a major virulence factor, shielding the bacterium from host phagocytosis and enabling immune evasion, including interference with opsonophagocytic killing even after release from the bacterial surface.[1][2][7][9] Serotype 3 strains, often in clonal complexes like CC180 (GPSC12) or emerging lineages such as GPSC10-ST700, drive severe pneumococcal infections including pneumonia and invasive disease, with unique recombination tendencies and capsule switching.[2][4][8] Vaccines like PCV13 and PPSV23 target CPS3 to elicit protective antibodies, though efficacy is challenged by variant CPS loci in resistant strains showing lower vaccine-induced killing.[2][4] Overall, CPS3 remains a key therapeutic target for pneumococcal vaccines due to its central role in pathogenesis.[2][9]

Other names

Type 3 capsular polysaccharideSerotype 3 CPSPn3 polysaccharide

Induction of opsonophagocytic antibodies against capsule and Capsule targeting to enhance phagocytosis and bacterial killing