L-type channel voltage-dependent facilitation results from asymmetric π-H and π-π quadrangle interactions at DI-DII domains

Voltage-dependent facilitation (VDF) is a distinctive phenomenon of L-type voltage-gated calcium (CaV) channels, in which depolarized prepulse voltages increase inward current by up to several fold. Despite extensive study, the molecular origin and biophysical mechanisms underlying the L-type channel (CaV1.1-CaV1.4) VDF remain elusive. A serendipitous observation that solutions stored in polypropylene tubes eliminated CaV1.2 and CaV1.3 L-type channel VDF led us to identify the leachable 2,4-di-tert-butylphenol (2,4-DTBP) as a selective VDF inhibitor. Docking and molecular dynamics simulations revealed previously unreported asymmetric {pi}-H and {pi}-{pi} interdomain quadrangle interactions at the DI-DII pore-domain (PD) interface in L-type channels. Disruption of these quadrangle interactions in CaV1.2 via point mutagenesis abolished the VDF. Whereas, introducing the quadrangle interaction onto non-VDF-displaying CaV<2.1 channels induced robust VDF. This work provides the first molecular evidence for the VDF endpoint: L-type channel-specific interdomain quadrangle interactions asymmetrically positioned at the DI-DII PD interface.