In its bound state PAK dimers are arranged in head-to-tail fashion and are maintained in inactive conformation in which the catalytic domain binds the kinase inhibitory (KI) domain.
All PAK family members are direct effectors of Rac1. Rac1 binds to a conserved Cdc42/Rac interactive binding (CRIB) domain in PAK1. This binding stimulates serine/threonine kinase activity of PAK1 by a mechanism involving autophosphorylation. Phosphorylation of S-144 and T-423 are required for the activation of PAK1. This phosphorylation disables the KI-domain-kinase interaction and thereby reduces the affinity of the PAK dimers.
Its been demonstarted that L1 stimulation propagates through VAV2-Rac1-Pak1 to MEK-ERK. It has been shown that Pak1 is able to phosphoarylate T292 and S298 on MEK, which is essential for the functional association of MEK with Raf.