title: Resolution of a low molecular weight G protein in neutrophil cytosol required for NADPH oxidase activation and reconstitution by recombinant Krev-1 protein.
abstract: Activation of the membrane-associated NADPH oxidase in intact human neutrophils requires a receptor-associated heterotrimeric GTP-binding protein that is sensitive to pertussis toxin. Activation of this NADPH oxidase by arachidonate in a cell-free system requires an additional downstream pertussis toxin-insensitive G protein (Gabig, T. G., English, D., Akard, L. P., and Schell, M. J. (1987) (J. Biol. Chem. 262, 1685-1690) that is located in the cytosolic fraction of unstimulated cells (Gabig, T. G., Eklund, E. A., Potter, G. B., and Dykes, J. R. (1990) J. Immunol. 145, 945-951). In the present study, immunodepletion of G proteins from the cytosolic fraction of unstimulated neutrophils resulted in a loss of the ability to activate NADPH oxidase in the membrane fraction. The activity in immunodepleted cytosol was fully reconstituted by a partially purified fraction from neutrophil cytosol that contained a 21-kDa GTP-binding protein. Purified human recombinant Krev-1 p21 also completely reconstituted immunodepleted cytosol whereas recombinant human H-ras p21 or yeast RAS GTP-binding proteins had no reconstitutive activity. Rabbit antisera raised against a synthetic peptide corresponding to the effector region of Krev-1 (amino acids 31-43) completely inhibited cell-free NADPH oxidase activation, and this inhibition was blocked by the synthetic 31-43 peptide. An inhibitory monoclonal antibody specific for ras p21 amino acids 60-77 (Y13-259) had no effect on cell-free NADPH oxidase activation. Activation of the NADPH oxidase in intact neutrophils by stimulation with phorbol myristate acetate caused a marked increase in the amount of membrane-associated antigen recognized by 151 antiserum on Western blot. Thus a G protein in the cytosol of unstimulated neutrophils antigenically and functionally related to Krev-1 may be the downstream effector G protein for NADPH oxidase activation. This system represents a unique model to study molecular interactions of a ras-like G protein.
authors.affiliation: Department of Medicine, Indiana University School of Medicine, Indianapolis 46202.
authors.forename: E A
authors.initials: EA
authors.lastname: Eklund
authors.forename: M
authors.initials: M
authors.lastname: Marshall
authors.forename: J B
authors.initials: JB
authors.lastname: Gibbs
authors.forename: C D
authors.initials: CD
authors.lastname: Crean
authors.forename: T G
authors.initials: TG
authors.lastname: Gabig
mesh_terms: D002474:Cell-Free System; D003600:Cytosol / Q000378:metabolism; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000302:isolation & purification / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D019255:NADPH Oxidases; D009504:Neutrophils / Q000737:chemistry / Q000201:enzymology*; D009841:Oligonucleotides / Q000737:chemistry; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D020668:rap GTP-Binding Proteins
chemical_list: D009841:Oligonucleotides; D011994:Recombinant Proteins; D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; D019204:GTP-Binding Proteins; D020668:rap GTP-Binding Proteins