Study Of The Molecular Mechanisms Of PIP₂’ Regulation On KCNQ2 Channel

Published studies of lipid-protein interactions have mainly focused on lipid binding to an individual site of the protein. Here, we show that a lipid can migrate between different binding sites in a protein and this migration modulates protein function. Voltage-gated potassium(Kv) channels have several potential binding sites for phosphatidylinositol-4,5-bisphosphate(PIP2). Our molecular dynamics(MD) simulations on the KCNQ2 channel reveal that PIP2 preferentially binds to the S4-S5 linker when the channel is in the open state while maintains a certain probability of migrating to the S2-S3 linker. Guided by the MD results, electrophysiological experiments using KCNQ2, KCNQ1, and h ERG channels show that the migration of PIP2 toward the S2-S3 linker controls the deactivation rate of the channel. The data suggest that PIP2 can migrate between different binding sites in Kv channels with significant impacts on channel deactivation, casting new insights into the dynamics and physiological functions of lipid-protein interactions.The S4-S5 linker in voltage-gated potassium(KV) channels mediates the coupling of the voltage sensor and the pore domain, which is critical for the response of KV channels to changes in membrane potential. PIP2, a minor lipid of the inner plasma membrane leaflet, has emerged as a key modulator of KV channel function. Recent analysis has indicated that PIP2-induced effects involve interactions with the S4-S5 linker(R214-K230) of KV channels, but the structural interactions with PIP2 at atomic level need further exploration. Here, using combined electrophysiological experiments and molecular dynamics(MD) simulations, we found that PIP2 simultaneously interacts with(i) K230 at the S4-S5 linker C-terminus in one chain and(ii) R214 and K219 in the S4-S5 linker N-terminus in the adjacent chain. This interaction stabilizes KCNQ2 in the open state; therefore, PIP2 acts as a structural determinant, cross-linking all four subunits and stabilizing the open state of KCNQ2. This work provides a deeper structural understanding of how the physiological modulation of PIP2 in turn modulates the gating mechanism of KV channels and, thereby affects cellular excitability.