title: Guanosine 5'-O-(3-thiotriphosphate) reduces ADP-ribosylation of the inhibitory guanine nucleotide-binding regulatory protein of adenylyl cyclase (Ni) by pertussis toxin without causing dissociation of the subunits of Ni. Evidence of existence of heterotrimeric pt+ and pt- conformations of Ni.
abstract: The effect of the addition of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), the GTP analog which activates the inhibitory guanine nucleotide-binding regulatory protein of adenylyl cyclase (Ni), on the pertussis toxin-mediated ADP-ribosylation reaction was studied in detail. Two effects were discerned: a stimulation of the ADP-ribosyltransferase activity of the toxin, akin to what was described for ATP and GDP in a previous report (Mattera, R., Codina, J., Sekura, R., and Birnbaumer, L. (1986) J. Biol. Chem. 261, 11173-11179), and a decrease in the ability of Ni to be a substrate for the activated toxin. Both effects were time-dependent with activation of the toxin being somewhat faster than inactivation of Ni. The effect of the addition of GTP gamma S on Ni was readily reversed by excess GDP and attenuated by increasing EDTA in the medium from 0.35 to 10 mM, suggesting dependence on trace concentrations of a divalent cation. It is suggested that this cation is Mg2+ on the basis that low (5-10 nM) concentrations of Mg2+ are needed for the endogenous GTPase activity of Ni (Sunyer, T., Codina, J., and Birnbaumer, L. (1984) J. Biol. Chem. 259, 15447-15451). Sucrose density gradient analysis of the Ni X GTP gamma S complexes with decreased susceptibility to ADP-ribosylation by pertussis toxin showed the same sedimentation parameters as Ni or Ni X GDP complexes, indicating that the molecule of Ni with GTP gamma S bound is heterotrimetric as opposed to dissociated into alpha i X GTP gamma S plus beta X gamma. Thus, these experiments define two conformations of heterotrimeric Ni: one -pt+, ADP-ribosylated by pertussis toxin, and the other pt-, poorly or not ADP-ribosylated by pertussis toxin. This latter, hitherto unrecognized conformation, is stabilized by the addition of strongly activating guanine nucleotides such as GTP gamma S and guanyl-5'-yl imidodiphosphate and should be important in the train of events that lead from an inactive heterotrimeric Ni to a fully active and dissociated Ni.
mesh_terms: D036002:ADP Ribose Transferases; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism*; D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000378:metabolism*; D002413:Cations, Divalent; D004492:Edetic Acid / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006153:Guanosine Diphosphate / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology; D010430:Pentosyltransferases / Q000378:metabolism; D037342:Pertussis Toxin; D011487:Protein Conformation; D013873:Thionucleotides / Q000494:pharmacology*; D010566:Virulence Factors, Bordetella / Q000378:metabolism*
chemical_list: D037361:Adenylate Cyclase Toxin; D002413:Cations, Divalent; D046911:Macromolecular Substances; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D006153:Guanosine Diphosphate; D000246:Adenosine Diphosphate Ribose; D006165:Guanylyl Imidodiphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D004492:Edetic Acid; D036002:ADP Ribose Transferases; D010430:Pentosyltransferases; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D008274:Magnesium