This domain forms an insert in bacterial beta-glucosidases and is found in other glycosidases, glycosyltransferases, proteases, amidases, yeast adhesins, and bacterial toxins, including anthrax protective antigen (PA). The domain also occurs in a Dictyostelium prespore-cell-inducing factor Psi and in fibrocystin, the mammalian protein whose mutation leads to polycystic kidney and hepatic disease. The crystal structure of PA shows that this domain (named PA14 after its location in the PA20 pro-peptide) has a beta-barrel structure. The PA14 domain sequence suggests a binding function, rather than a catalytic role. The PA14 domain distribution is compatible with carbohydrate binding.