Escherichia coli colonization factor antigen CS6 (CS6)

Escherichia coli colonization factor antigen CS6 is a major non-fimbrial surface adhesin expressed by enterotoxigenic *Escherichia coli* (ETEC), a leading bacterial cause of diarrheal disease, especially in children in developing countries and travelers[2][6][7]. CS6 is a heteropolymeric protein complex composed of two major subunits, CssA and CssB, which are assembled on the bacterial surface via the chaperone/usher pathway (CssC and CssD)[1][5][7]. These subunits alternate to form linear or oligomeric structures that mediate ETEC’s initial attachment to the small intestinal epithelium. CssA primarily mediates binding to the host extracellular matrix protein fibronectin via a C-terminal region, while CssB binds sulfatide, a glycosphingolipid abundant in human small intestine[2][6][7]. The adhesive function of CS6 is critical for effective colonization and disease pathogenesis, making it a key vaccine target to prevent ETEC infection[3][7]. CS6 does not have known enzymatic or signaling functions but plays a direct structural role in host-pathogen interaction. Variants of CS6 occur due to point mutations in subunits, which may influence ETEC pathogenicity[4]. CS6 expression is associated with increased risk of infectious diarrhea, but its absence of enzymatic activity limits its role as a direct drug target outside of its function as a vaccine antigen. There are currently no approved drugs targeting CS6, but experimental vaccines and antibody-mediated strategies are under evaluation[3].

Other names

Coli surface antigen 6CFA/IVColonization factor antigen 6CS6 colonization factor

Drugs and vaccines targeting CS6 would block its adhesive function—preventing ETEC from binding to host gut epithelium[3] Antibody-mediated inhibition of colonization through blocking subunit interactions with host ligands (fibronectin, sulfatide)[2][6][7]