Asymmetric Contribution of a Selectivity Filter Gate in Triggering Inactivation of Ca_V1.3 Channels

Voltage-dependent and Ca²⁺-dependent inactivation (VDI and CDI, respectively) of Ca_V channels are two biologically consequential feedback mechanisms that fine-tune Ca²⁺ entry into neurons and cardiomyocytes. Although known to be initiated by distinct molecular events, how these processes obstruct conduction through the channel pore remains poorly defined. Here, focusing on ultra-highly conserved tryptophan residues in the inter-domain interfaces near the selectivity filter of Ca_V1.3, we demonstrate a critical role for asymmetric conformational changes in mediating VDI and CDI. Specifically, mutagenesis of the domain III-IV interface, but not others, enhanced VDI. Molecular dynamics simulations demonstrate that mutations in distinct selectivity filter interfaces differentially impact conformational flexibility. Furthermore, mutations in distinct domains preferentially disrupt CDI mediated by the N- versus C-lobes of CaM, thus uncovering a scheme of structural bifurcation of CaM signaling. These findings highlight the fundamental importance of the asymmetric arrangement of the pseudo-tetrameric Ca_V pore domain for feedback inhibition.