Binding Site and Inhibitory Mechanism of the Mambalgin-2 Pain-relieving Peptide on Acid-sensing Ion Channel 1a*

Acid-sensing ion channels (ASICs) are neuronal proton-gated cation channels associated with nociception, fear, depression, seizure, and neuronal degeneration, suggesting roles in pain and neurological and psychiatric disorders. We have recently discovered black mamba venom peptides called mambalgin-1 and mambalgin-2, which are new three-finger toxins that specifically inhibit with the same pharmacological profile ASIC channels to exert strong analgesic effects in vivo. We now combined bioinformatics and functional approaches to uncover the molecular mechanism of channel inhibition by the mambalgin-2 pain-relieving peptide. Mambalgin-2 binds mainly in a region of ASIC1a involving the upper part of the thumb domain (residues Asp-349 and Phe-350), the palm domain of an adjacent subunit, and the β-ball domain (residues Arg-190, Asp-258, and Gln-259). This region overlaps with the acidic pocket (pH sensor) of the channel. The peptide exerts both stimulatory and inhibitory effects on ASIC1a, and we propose a model where mambalgin-2 traps the channel in a closed conformation by precluding the conformational change of the palm and β-ball domains that follows proton activation. These data help to understand inhibition by mambalgins and provide clues for the development of new optimized blockers of ASIC channels.