Structural basis for human Ca1.2 inhibition by multiple drugs and the neurotoxin calciseptine.

Ca1.2 channels play crucial roles in various neuronal and physiological processes. Here, we present cryo-EM structures of human Ca1.2, both in its apo form and in complex with several drugs, as well as the peptide neurotoxin calciseptine. Most structures, apo or bound to calciseptine, amlodipine, or a combination of amiodarone and sofosbuvir, exhibit a consistent inactivated conformation with a sealed gate, three up voltage-sensing domains (VSDs), and a down VSD. Calciseptine sits on the shoulder of the pore domain, away from the permeation path. In contrast, when pinaverium bromide, an antispasmodic drug, is inserted into a cavity reminiscent of the IFM-binding site in Na channels, a series of structural changes occur, including upward movement of VSD coupled with dilation of the selectivity filter and its surrounding segments in repeat III. Meanwhile, S4-5 merges with S5 to become a single helix, resulting in a widened but still non-conductive intracellular gate.