Scorpion toxin inhibits the voltage-gated proton channel using a Zn 2+ -like long-range conformational coupling mechanism.

Background and Purpose Blocking the voltage-gated proton channel H(V)1 is a promising strategy for the treatment of diseases like ischaemia stroke and cancer. However, few H(V)1 channel antagonists have been reported. Here, we have identified a novel H(V)1 channel antagonist from scorpion venom and have elucidated its action mechanism. Experimental Approach H(V)1 and NaV channels were heterologously expressed in mammalian cell lines and their currents recorded using whole-cell patch clamp. Site-directed mutagenesis was used to generate mutants. Toxins were recombinantly produced in Escherichia coli. AGAP/W38F-H(V)1 interaction was modelled by molecular dynamics simulations. Key Results The scorpion toxin AGAP (anti-tumour analgesic peptide) potently inhibited H(V)1 currents. One AGAP mutant has reduced Na-V channel activity but intact H(V)1 activity (AGAP/W38F). AGAP/W38F inhibited H(V)1 channel activation by trapping its S4 voltage sensor in a deactivated state and inhibited H(V)1 currents with less pH dependence than Zn2+. Mutation analysis showed that the binding pockets of AGAP/W38F and Zn2+ in H(V)1 channel partly overlapped (common sites are His140 and His193). The E153A mutation at the intracellular Coulombic network (ICN) in H(V)1 channel markedly reduced AGAP/W38F inhibition, as observed for Zn2+. Experimental data and MD simulations suggested that AGAP/W38F inhibited H(V)1 channel using a Zn2+-like long-range conformational coupling mechanism. Conclusion and Implications Our results suggest that the Zn2+ binding pocket in H(V)1 channel might be a hotspot for modulators and valuable for designing H(V)1 channel ligands. Moreover, AGAP/W38F is a useful molecular probe to study H(V)1 channel and a lead compound for drug development.