Schematic diagram of the domain structure of integrin β subunits. Domain arrangement is based on crystal structures of the extracellular regions of α Vβ3 , α IIbβ3  and β2 . PSI, plexin/semaphorin/integrin; EGF, epidermal growth factor; TM, transmembrane. N-, amino terminus; C-, carboxyl terminus. Dotted line indicates the overall path of the polypeptide chain.