Integrins have been found in animals and their homologues have also been found in cyanobacteria, probably due to horizontal gene transfer [1]. This domain corresponds to the integrin beta VWA domain.

1: Integrin alpha- and beta 4-subunit-domain homologues in cyanobacterial proteins. May AP, Ponting CP; Trends Biochem Sci 1999;24:12-13. PMID:10087915