Fig. 4: Ceramides induce hERG1 block by a conformational selection mechanism through a lipophilic pathway.

CER6 molecules partition into the membrane (after their application to the external milieu), followed by preferential binding to the interface between the voltage-sensing domain (VSD, green color) and the pore domain (PD, gray color) of hERG1 channels displaying a closed-state PD (only one of the four VSD–PD interfaces is shown). As a result, ceramides shift the population of hERG1A-WT channels towards the closed state (conformational selection), accelerating channel deactivation kinetics (left-pointing black arrow). The mutations hERG1A-F656C and F656C/F557L (right-pointing red arrow) affect ceramide interactions at the VSD–PD interface and induce slower channel deactivation kinetics, favoring the open state of the channel and the occurrence of residual currents (lack of complete channel block). In contrast, the mutation hERG1A-Y652A and the truncated N-terminal region in hERG1B isoform (left-pointing red arrow) induce faster deactivation kinetics, resulting in a higher population of ceramide-bound channels with closed-state PD and the lack of residual currents. Only two states are represented in this mechanism, corresponding to the two hERG1 channel structures used for MD simulations in this work: closed-state PD (homology model based on EAG Cryo-EM structure⁷, left) and open-state PD (hERG1 Cryo-EM structure¹⁰, right). Transitions at the VSD during activation and deactivation are not represented due to current structural-model limitations (see discussion). The ion permeation pathway in the PD of the channel is shown in blue color. Generic plasma-membrane phospholipids’ headgroups and tails are colored in orange and gray colors, respectively.