title: Purification and characterization of Rac 2. A cytosolic GTP-binding protein that regulates human neutrophil NADPH oxidase.
abstract: Human neutrophils and other phagocytes generate superoxide anion (O2-) as a means of destroying ingested microorganisms. O2- is produced by an NADPH-consuming oxidase composed of membrane and cytosolic components. Activation of the NADPH oxidase is absolutely dependent upon GTP, indicating the requirement for a GTP-binding protein in this process. We have utilized a five-step chromatographic procedure to isolate a GTP-binding protein from human neutrophil cytosol which can stimulate NADPH oxidase activity in a cell-free assay. Oxidase enhancing activity was shown to coisolate with this GTP-binding component, which was purified to apparent homogeneity. The GTP-binding protein was identified as Rac 2 by immunological reactivity and amino acid sequencing. Thus, Rac 2 appears to be a third cytosolic component required for human neutrophil NADPH oxidase activation. Recombinant Rac 2 was shown to bind guanine nucleotides in a Mg(2+)-dependent fashion. GDP dissociation rates were determined and shown to be regulated by the free Mg2+ concentration. Rac 2 was found to possess the highest rate of intrinsic GTP hydrolysis of any of the characterized members of the Ras superfamily. The biochemical properties of Rac 2 indicate it is likely to be subject to regulatory cofactors in vivo.
authors.affiliation: Department Immunology and Cell Biology, Scripps Research Institute, La Jolla, California 92037.
authors.forename: U G
authors.initials: UG
authors.lastname: Knaus
authors.forename: P G
authors.initials: PG
authors.lastname: Heyworth
authors.forename: B T
authors.initials: BT
authors.lastname: Kinsella
authors.forename: J T
authors.initials: JT
authors.lastname: Curnutte
authors.forename: G M
authors.initials: GM
authors.lastname: Bokoch
mesh_terms: D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D003600:Cytosol / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D020558:GTP Phosphohydrolases / Q000097:blood* / Q000302:isolation & purification*; D019204:GTP-Binding Proteins / Q000302:isolation & purification* / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D009247:NADH, NADPH Oxidoreductases / Q000097:blood*; D019255:NADPH Oxidases; D009504:Neutrophils / Q000378:metabolism*; D013481:Superoxides / Q000097:blood; D020744:rac GTP-Binding Proteins
chemical_list: D013481:Superoxides; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020744:rac GTP-Binding Proteins; D008274:Magnesium