Voltage-Sensor Pharmacology Of Calcium Channels

Voltage-gated calcium (Cav) channels contain four homologous domains, presenting the possibility of multiple toxin binding sites. Studies of related voltage-gated potassium (Kv) channels identified the S3b-S4 structural motif, which moves at the protein-lipid interface to drive voltage-sensor activation, as the pharmacological target for amphipathic neurotoxins. Here we show that the homologous S3b-S4 sequences within the Cav2 and Cav3 families can be transplanted into the homotetrameric Kv channel to individually examine their contributions to voltage sensor activation and pharmacology. We found that the four Cav motifs display distinct toxin binding properties. We also identified the molecular surfaces involved in the toxin-channel interaction. Furthermore, as gating-modifiers of Kv channels have been shown to favor binding to the lipid bilayer prior to binding to the channel, we probed the lipid partitioning capabilities of Cav toxins, using intrinsic tryptophan fluorescence. Our results indicate a strong correlation between the strength of lipid partitioning and channel inhibition.