title: Pak1 kinase homodimers are autoinhibited in trans and dissociated upon activation by Cdc42 and Rac1.
abstract: Pak1, a serine/threonine kinase that regulates the actin cytoskeleton, is an effector of the Rho family GTPases Cdc42 and Rac1. The crystal structure of Pak1 revealed an autoinhibited dimer that must dissociate upon GTPase binding. We show that Pak1 forms homodimers in vivo and that its dimerization is regulated by the intracellular level of GTP-Cdc42 or GTP-Rac1. The dimerized Pak1 adopts a trans-inhibited conformation: the N-terminal inhibitory portion of one Pak1 molecule in the dimer binds and inhibits the catalytic domain of the other. One GTPase interaction can result in activation of both partners. Another ligand, betaPIX, can stably associate with dimerized Pak1. Dimerization does not facilitate Pak1 trans-phosphorylation. We conclude that the functional significance of dimerization is to allow trans-inhibition.
authors.affiliation: Laboratory of Molecular Medicine, Boston, MA 02115, USA. parini@rascal.med.harvard.edu
authors.forename: Maria Carla
authors.initials: MC
authors.lastname: Parrini
authors.forename: Ming
authors.initials: M
authors.lastname: Lei
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Harrison
authors.forename: Bruce J
authors.initials: BJ
authors.lastname: Mayer
mesh_terms: D000595:Amino Acid Sequence; D018797:Cell Cycle Proteins / Q000378:metabolism; D002460:Cell Line; D019281:Dimerization; D004789:Enzyme Activation; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D006801:Humans; D008024:Ligands; D008969:Molecular Sequence Data; D009154:Mutation; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D064067:Rho Guanine Nucleotide Exchange Factors; D014162:Transfection; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*; D054462:p21-Activated Kinases; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D008024:Ligands; D064067:Rho Guanine Nucleotide Exchange Factors; C515903:PAK1 protein, human; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein