Heteromeric Assembly of Human M-Channels
Co-expression of KCNQ2 and KCNQ3 yielded functional M-channels with robust macroscopic currents. Cryo-EM analysis uncovered an unexpected assembly landscape, with the channel predominantly adopting a 3:1 KCNQ2 to KCNQ3 stoichiometry alongside a minor staggered 2:2 form (Figure 1). These findings reveal a highly ordered yet adaptable assembly mode and provide the structural framework for understanding the organization and function of heteromeric ion channels.
KCNQ3 Drives Low-Threshold Activation
Why does the M-channel activate near the neuronal resting potential? Structural comparison indicated that the voltage-sensing domain (VSD) of KCNQ3 preferentially adopts an ‘up’ or activated conformation relative to KCNQ2. To test this, the authors replaced all VSDs in the heteromeric channel with those from KCNQ3, resulting in a pronounced shift of channel activation toward more negative voltages (Figure 2). These results identify KCNQ3 as the principal determinant of low-threshold gating, tuning the M-channel to suppress neuronal firing at physiological membrane potentials.
Drug Recognition and Cooperative Gating
The study further dissects the mechanisms of action (MOAs) of two structurally distinct M-channel modulators. ICA-110381 selectively binds to the VSD of KCNQ2, and the atomic-resolution structures explain its subunit specificity while independently validating the arrangement of KCNQ2 subunits within the heteromeric complexes (Figure 3).
In contrast, XEN1101, a Phase III antiepileptic candidate, occupies a conserved fenestration site within the pore domain (PD). Strikingly, multiple intermediate states reveal that XEN1101 acts cooperatively with the endogenous phospholipid PIP2 to promote channel opening through a stepwise activation process (Figure 4), providing direct evidence for lipid-drug cooperativity in regulating M-channel gating.
Together, these findings fill a longstanding gap in the KCNQ field and provide an atomic-level framework for understanding heteromeric M-channel assembly, gating, and pharmacological modulation. Beyond advancing fundamental knowledge, the work establishes a structural foundation for the development of next-generation antiepileptic therapies with improved subtype selectivity, efficacy, and safety profile, offering new opportunities for the treatment of developmental and epileptic encephalopathies (DEE) and other KCNQ-related channelopathies.
doi:10.15302/vita.2026.05.0035.