title: Mastoparan, a peptide toxin from wasp venom, mimics receptors by activating GTP-binding regulatory proteins (G proteins).
abstract: Mastoparan, a peptide toxin from wasp venom, is a nonspecific secretagogue. We show here that mastoparan increases the GTPase activity and the rate of nucleotide binding of several purified GTP-binding regulatory proteins (G proteins) whose function is to couple cell-surface receptors to intracellular mediators. Mastoparan accelerated guanosine-5'-(3-O-thiotriphosphate binding and consequent G protein activation in part by promoting the dissociation of bound GDP, the mechanism by which receptors regulate G proteins. ADP-ribosylation by pertussis toxin, which uncouples receptors from G proteins, selectively inhibited mastoparan-stimulated activation. Like receptors, mastoparan was more potent if the G protein was reconstituted in phospholipid vesicles and was active at micromolar concentrations of Mg2+. The structure of mastoparan in a lipid bilayer is similar to that predicted for a cationic intracellular loop of G protein-coupled receptors. Mastoparan thus displays a novel mode of toxicity by acting directly on G proteins to mimic the role normally played by agonist-liganded receptors.
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D001514:Bee Venoms / Q000494:pharmacology*; D001921:Brain / Q000378:metabolism; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D010455:Peptides; D037342:Pertussis Toxin; D011817:Rabbits; D011955:Receptors, Drug / Q000187:drug effects / Q000378:metabolism; D013873:Thionucleotides / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014862:Wasp Venoms / Q000494:pharmacology*
chemical_list: D001514:Bee Venoms; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D011955:Receptors, Drug; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D014862:Wasp Venoms; D000246:Adenosine Diphosphate Ribose; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C037500:mastoparan; D006160:Guanosine Triphosphate; D037342:Pertussis Toxin; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins