This domain family is found in bacteria and viruses, and is approximately 80 amino acids in length.This domain is the beta barrel domain of bacteriophage endosialidase which represents the one of the two sialic acid binding sites of the enzyme. The domain is nested in the beta propeller domain of the endosialidase enzyme. The endosialidase protein complexes to form homotrimeric molecules.

1: Crystal structure of the polysialic acid-degrading endosialidase of bacteriophage K1F. Stummeyer K, Dickmanns A, Muhlenhoff M, Gerardy-Schahn R, Ficner R; Nat Struct Mol Biol. 2005;12:90-96. PMID:15608653