Identification of a novel snake peptide toxin displaying high affinity and antagonist behaviour for the α(2) -adrenoceptors.
Résumé
Background and purpose. Muscarinic and adrenergic G-protein coupled receptors (GPCRs) are the targets of rare peptide toxins isolated from snake or cone snail venoms. We used a screen to identify novel toxins from Dendroaspis angusticeps targeting aminergic GPCRs. These toxins may offer new candidates for the development of new tools and drugs. Experimental approach. In binding experiments with (3) H-rauwolscine, we studied the interactions of green mamba venom fractions with α(2) -adrenoceptors from rat brain synaptosomes. We isolated, sequenced and chemically synthesized a novel peptide, ρ-Da1b. This peptide was pharmacologically characterized using binding experiments and functional tests on human α(2) -adrenoceptors expressed in mammalian cells. Key results. ρ-Da1b, a 66 amino-acid peptide stabilized by four disulfide bridges, belongs to the three-finger fold peptide family. Its synthetic homologue inhibited 80 % of (3) H-rauwolscine binding to the three α(2) -adrenoceptor subtypes, with an affinity between 14 and 73 nM and Hill slopes close to unity. Functional experiments on α(2A) -adrenoceptor demonstrated that ρ-Da1b is an antagonist, shifting adrenaline activation curves to the right. Schild regression revealed slopes of 0.97 and 0.67 and pA(2) values of 5.93 and 5.32 for yohimbine and ρ-Da1b, respectively. Conclusions and implications. ρ-Da1b is the first toxin identified to specifically interact with α(2) -adrenoceptors, extending the list of class A GPCRs sensitive to toxins. Additionally, its affinity and atypical mode of interaction open up the possibility of its use as a new pharmacological tool, in the study of the physiological roles of α(2) -adrenoceptor subtypes.