CssAB is a family of CS6 pilins from E.coli, including both subunits A and B. It acts as a colonisation factor for the enterotoxigenic species pf E.coli to mediate bacterial attachment to the small intestinal epithelium. Both subunits in the fibre bind to receptors on epithelial cells, and that CssB, but not CssA, specifically recognises the extracellular matrix protein fibronectin [1].

1: Crystal structure of enterotoxigenic Escherichia coli colonization factor CS6 reveals a novel type of functional assembly. Roy SP, Rahman MM, Yu XD, Tuittila M, Knight SD, Zavialov AV; Mol Microbiol. 2012;86:1100-1115. PMID:23046340