New α-adrenergic property for synthetic MTβ and CM-3 three-finger fold toxins from black mamba

Despite their isolation more than fifteen years ago from the venom of the African mamba Dendroaspis polylepis, very few data are known on the functional activity of MTb and CM-3 toxins. MTb was initially classified as a muscarinic toxin interacting non-selectively and with low affinity with the five muscarinic receptor subtypes while no biological function was determined for CM-3. Recent results highlight the multifunctional activity of threefinger fold toxins for muscarinic and adrenergic receptors and reveal some discrepancies in the pharmacological profiles of their venom-purified and synthetic forms. Here, we report the pharmacological characterization of chemically-synthesized MTb and CM-3 toxins on nine subtypes of muscarinic and adrenergic receptors and demonstrate their high potency for a-adrenoceptors and in particular a sub-nanomolar affinity for the a1Asubtype. Strikingly, no or very weak affinity were found for muscarinic receptors, highlighting that pharmacological characterizations of venom-purified peptides may be risky due to possible contaminations. The biological profile of these two homologous toxins looks like that one previously reported for the Dendroaspis angusticeps r-Da1a toxin. Nevertheless, MTb and CM-3 interact more potently than r-Da1a with a1B- and a1D-AR subtypes. A computational analysis of the stability of the MTb structure suggests that mutation S38I, could be involved in this gain in function.