<p>Integrins are cell adhesion molecules that mediate cell-extracellular matrix and cell-cell interactions. They contain both alpha and beta subunits. Alpha integrins are proposed to contain a domain containing a 7-fold repeat that adopts a beta-propellor fold. Some of these domains contain an inserted von Willebrand factor type-A domain. Some repeats contain putative calcium-binding sites. The 7-fold repeat domain is homologous to a similar domain in phosphatidylinositol-glycan-specific phospholipase D.</p>