DDEF2 (ADP ribosylation factor [ARF]- GTPase-activating protein [GAP] containing SH3, ANK repeats, and PH domain, PAP, PAG3, AMAP1, ZG14P, centaurin beta4) is a phospholipid-dependent ADP-ribosylation factor (ARF) GTPase-activating protein (ARF-GAP) that binds to protein-tyrosine kinases Src and focal adhesion kinase. ARF family GTP-binding proteins are regulators of membrane traffic and cytoskeletal organization. Modulation of ARF activity by DDEF2 is important for the regulation of focal adhesion assembly and/or organization by influencing the mechanisms responsible for the recruitment and organization of focal adhesion proteins paxillin and FAK. In spreading platelets, most endogenous DDEF2 is localized at peripheral focal adhesions. Pyk2 directly phosphorylates DDEF2 on tyrosine-308 and -782, and this event affects the phosphoinositide binding profile of DDEF2. DDEF2 is phosphorylated on tyrosine residues in cells expressing activated Src and tyrosine phosphorylation depends on a proline-rich class II Src SH3 binding site.