The M-channel, a voltage-gated potassium channel composed of KCNQ2 and KCNQ3 subunits, is a master regulator of neuronal excitability^1-3. Its unique ability to activate at voltages below the action potential threshold allows it to dampen repetitive firing and stabilize the resting membrane potential^4-6. Mutations in KCNQ2 or KCNQ3 cause a spectrum of severe neurological disorders, including benign familial neonatal seizures (BFNS)^7-9 and developmental and epileptic encephalopathy type 7 (DEE7)^9,10, making the M-channel a long-standing therapeutic target. However, fundamental questions — including its subunit stoichiometry, the origin of its exquisite voltage sensitivity, and how to selectively enhance its activity — have persisted for decades.
Now, Shen's team at Westlake University, in collaboration with Yang's team at East China Normal University, have tackled these questions head-on. Using cryo-electron microscopy, they resolved the structures of the human M-channel in multiple functional states, revealing its architectural principles and translating these insights into a rational drug design strategy.
The M-channel displays remarkable stoichiometric plasticity: rather than adopting a fixed 2:2 ratio of KCNQ2 to KCNQ3, all possible configurations from 1:3 to 3:1 coexist, with their relative abundance shifting according to subunit expression levels (Fig.1). Engineered concatemers confirmed that each configuration generates functional M-currents, suggesting neurons may tune channel properties by adjusting subunit availability.
The M-channel, a voltage-gated potassium channel composed of KCNQ2 and KCNQ3 subunits, is a master regulator of neuronal excitability^1-3. Its unique ability to activate at voltages below the action potential threshold allows it to dampen repetitive firing and stabilize the resting membrane potential^4-6. Mutations in KCNQ2 or KCNQ3 cause a spectrum of severe neurological disorders, including benign familial neonatal seizures (BFNS)^7-9 and developmental and epileptic encephalopathy type 7 (DEE7)^9,10, making the M-channel a long-standing therapeutic target. However, fundamental questions — including its subunit stoichiometry, the origin of its exquisite voltage sensitivity, and how to selectively enhance its activity — have persisted for decades.
Now, Shen's team at Westlake University, in collaboration with Yang's team at East China Normal University, have tackled these questions head-on. Using cryo-electron microscopy, they resolved the structures of the human M-channel in multiple functional states, revealing its architectural principles and translating these insights into a rational drug design strategy.
The M-channel displays remarkable stoichiometric plasticity: rather than adopting a fixed 2:2 ratio of KCNQ2 to KCNQ3, all possible configurations from 1:3 to 3:1 coexist, with their relative abundance shifting according to subunit expression levels (Fig.1). Engineered concatemers confirmed that each configuration generates functional M-currents, suggesting neurons may tune channel properties by adjusting subunit availability.
Leveraging the resolved structures, the team developed CLM142, a next-generation activator ten times more potent than retigabine and highly selective for the KCNQ2/KCNQ3 heteromer (Fig.3), with cryo-EM revealing it nestles into the S5–S6 pocket via a key π-π interaction and hydrophobic sub-pocket anchoring. They further captured the fully open state stabilized by CLM142 and PIP₂, where PIP₂ bridges the VSD and pore domain through basic residues, coupling voltage-sensor movement to S6 rotation and pore dilation (Fig.4).
This work resolves the long-standing mysteries of M-channel assembly and gating, while also providing a template for developing selective ion channel modulators. By demonstrating that subunit composition is flexible and driven by expression levels, the findings suggest that neurons may naturally exploit stoichiometric variation to fine-tune excitability. Moreover, the structure-based design of CLM142 charts a path toward safer antiepileptic therapies that specifically target the M-channel without the toxicities that plagued earlier drugs. Beyond epilepsy, the principles uncovered here may illuminate how other heteromeric ion channels achieve their physiological specialization.
DOI：10.15302/vita.2026.05.0032