Abstract: The invention relates to polypeptides which form a protein complex which regulates cytoskeletal reorganization, for example, in connection with T cell activation. The invention also relates to nucleic acids that encode the polypeptides, as well as agents which bind the nucleic acids or the encoded polypeptides. Also disclosed are methods of using such nucleic acids, polypeptides and binding agents to modulate protein complex formation, actin cytoskeletal reorganization and cell activity, as well as drug discovery methods.