Activation-dependent carboxyl methylation of neutrophil G-protein gamma subunit.
The gamma subunits of heterotrimeric guanine nucleotide-binding regulatory (G) proteins (G gamma) are post-translationally processed at their C termini by prenylation, proteolysis, and carboxyl methylation. Whereas prenylation of G gamma is required for membrane association of G proteins, the role of carboxyl methylation is unknown. Here we show that human neutrophils express G gamma 2 but not G gamma 3 or G gamma 7 and that carboxyl methylation of G gamma 2 is associated with signal transduction. In a reconstituted cell-free system, neutrophil G gamma 2 was labeled by the methyl donor S-[methyl-3H]adenosyl-L-methionine. Carboxyl methylation was confirmed by alkaline hydrolysis and quantitation of volatile [3H]methanol. Neutrophil G gamma 2 methylation was stimulated by activation of G protein with guanosine 5'-[beta, gamma-thio]triphosphate. We estimate that after 1 hr of G-protein activation at least 6% of the total pool of G gamma 2 was carboxyl-methylated. The inflammatory agonist fMet-Leu-Phe stimulated guanosine 5'-[beta,gamma-thio]triphosphate-dependent carboxyl methylation. Methylation of G gamma 2 was inhibited by the carboxyl methyltransferase inhibitor N-acetyl-S-trans,trans-farnesylcysteine at concentrations that affected signal transduction in neutrophils. These results demonstrate that activation of neutrophil Gi is associated with alpha-carboxyl methyl esterification of G gamma 2 and suggest that carboxyl methylation of G gamma may play a role in signal transduction.
Philips
M R
MR
Department of Medicine, New York University Medical Center, NY 10016.
Staud
R
R
Pillinger
M
M
Feoktistov
A
A
Volker
C
C
Stock
J B
JB
Weissmann
G
G
D000906:Antibodies; D004591:Electrophoresis, Polyacrylamide Gel; D019204:GTP-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D006150:Guanine Nucleotides / Q000494:pharmacology; D006801:Humans; D015151:Immunoblotting; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D046911:Macromolecular Substances; D008745:Methylation; D008970:Molecular Weight; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D012436:S-Adenosylmethionine / Q000378:metabolism*; D014316:Tritium
D000906:Antibodies; D006150:Guanine Nucleotides; D007457:Iodine Radioisotopes; D046911:Macromolecular Substances; D014316:Tritium; D009240:N-Formylmethionine Leucyl-Phenylalanine; D012436:S-Adenosylmethionine; D019204:GTP-Binding Proteins