title: Rac "insert region" is a novel effector region that is implicated in the activation of NADPH oxidase, but not PAK65.
abstract: The small GTPase Rac assembles with the cytosolic p47(phox) and p67(phox) and the membrane-associated flavocytochrome b558 to form the multicomponent respiratory burst oxidase. Mutation of amino acids in a region of Rac (residues 26-45), homologous to an effector region in Ras, was previously shown to interfere with Rac binding to the oxidase. Herein we have elucidated an additional region in Rac involved in regulating oxidase activity. Rho family small GTPases contain a 12-amino acid "insert" region (residues 124-135) that is not present in Ras. Point mutations in and deletion of this region were constructed and used for in vitro studies of the activation of PAK65 and NADPH oxidase. Apparent binding constants (based on EC50 values) of the mutant Rac proteins for the oxidase are at least 13-25-fold higher than for wild-type Rac. Mutations in the insert region versus the 26-45 effector region resulted in distinct kinetic consequences, pointing to different roles for these two protein regions: mutations in the insert region but not the 26-45 effector region resulted in an increase in the EC50 for p67(phox). Although mutations in the 26-45 amino acid effector region showed markedly diminished activation of both PAK and the NADPH oxidase, insert region mutations did not affect activation of PAK. We propose that the combinatorial use of the 26-45 effector region and the insert region provides the Rho family GTPases with versatility in their specificity for several downstream targets.
authors.affiliation: Department of Biochemistry, Emory University Medical School, Atlanta, Georgia 30322, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Freeman
authors.forename: A
authors.initials: A
authors.lastname: Abo
authors.forename: J D
authors.initials: JD
authors.lastname: Lambeth
mesh_terms: D000595:Amino Acid Sequence; D002474:Cell-Free System; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D006150:Guanine Nucleotides / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D019255:NADPH Oxidases; D009504:Neutrophils / Q000201:enzymology; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D016897:Respiratory Burst; D019893:Ribosomal Protein S6 Kinases; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D013481:Superoxides / Q000378:metabolism; D020744:rac GTP-Binding Proteins
chemical_list: D006150:Guanine Nucleotides; D013481:Superoxides; D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D019204:GTP-Binding Proteins; D020744:rac GTP-Binding Proteins