Serine/threonine-protein kinase PAK1 (PAK1) exists as homodimer in a trans-inhibited conformation. PAK1 translocates from cytosol to plasma membrane and comes in close proximity to RAC1. The kinase inhibitory (KI) domain of one PAK1 molecule binds to the C-terminal catalytic domain of the other and inhibits catalytic activity. RAC1:GTP bind to the GBD domain of PAK1 thereby altering the conformation of the KI domain, relieving inhibition of its catalytic domain, and allowing PAK1 autophosphorylation that is required for full kinase activity (Parrini et al. 2002, Zhao & Manser 2005, Sells et al. 2000).