Requirement for posttranslational processing of Rac GTP-binding proteins for activation of human neutrophil NADPH oxidase.
Rac1 and Rac2 are closely related, low molecular weight GTP-binding proteins that have both been implicated in regulation of phagocyte NADPH oxidase. This enzyme system is composed of multiple membrane-bound and cytosolic subunits and when activated catalyzes the one-electron reduction of oxygen to superoxide. Superoxide and its highly reactive derivatives are essential for killing microorganisms. Rac proteins undergo posttranslational processing, primarily the addition of an isoprenyl group to a carboxyl-terminal cysteine residue. We directly compared recombinant Rac1 and Rac2 in a human neutrophil cell-free NADPH oxidase system in which cytosol was replaced by purified recombinant cytosolic components (p47-phox and p67-phox). Processed Rac1 and Rac2 were both highly active in this system and supported comparable rates of superoxide production. Under different cell-free conditions, however, in which suboptimal amounts of cytosol were present in the assay mixture, processed Rac2 worked much better than Rac1 at all but the lowest concentrations. This suggests that a factor in the cytosol may suppress the activity of Rac1 but not of Rac2. Unprocessed Rac proteins were only weakly able to support superoxide generation in either system, but preloading of Rac1 or Rac2 with guanosine 5'-O-(3-thio-triphosphate) (GTP gamma S) restored activity. These results indicate that processing is required for nucleotide exchange but not for interaction with oxidase components.
Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, California 92037.
P G
PG
Heyworth
U G
UG
Knaus
X
X
Xu
D J
DJ
Uhlinger
L
L
Conroy
G M
GM
Bokoch
J T
JT
Curnutte
D000595:Amino Acid Sequence; D003600:Cytosol / Q000378:metabolism; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D019255:NADPH Oxidases; D009504:Neutrophils / Q000201:enzymology*; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D020744:rac GTP-Binding Proteins
D011994:Recombinant Proteins; D013481:Superoxides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; D019204:GTP-Binding Proteins; D020744:rac GTP-Binding Proteins