Ion channels facilitate the ‘electrical signals of life’ by opening, closing, and desensitizing to regulate the flow of ions across the cellular membrane. The Kv7 is one such family of ion channels that conducts Potassium ion efflux in response to a depolarization of the transmembrane potential. Five isoforms termed Kv7.1 to Kv7.5 makeup this family of channels and are ubiquitously distributed across a range of tissues. The proteins play a role in multiple physiological processes and are implicated in a range of disorders including long-QT syndrome, epilepsy, deafness, and loss of bladder control. Despite this prevalence of Kv7-associated disorders, no approved pharmaceutical intervention targeted at the channels exists. In fact, the only two approved Kv7 channel openers – Retigabine and Flupirtine were both withdrawn due to undesirable off-target effects.
Traditionally, this challenge in the development of Kv7 pharmaceutics was attributed to the significant sequence and structural homogeneity among the five isoforms resulting in a lack of drug specificity. However, the spate of newly resolved cryo-EM structures together with advances electrophysiological techniques have helped unveil a multitude of channelopathies affecting different aspects of the channel’s conformational cycle. Mutations within the voltage-sensing domain can affect voltage-sensitivity, those within the S4-S5 linker can affect coupling between protein domains and those within the pore domain can affect open probability or PIP2 sensitivity. Thus, drugs targeting the Kv7 voltage-gated ion channels require both (i) subtype- and (ii) channelopathy-specificity.
Through the combination of computational and experimental methods, the group has made significant headway into the first challenge of subtype-specificity by identifying four molecular scaffolds capable of selectively modulating the Kv7 voltage-gated ion channels. (1) Endocannabinoids bind to the Kv7.1 channel to augment function. (2) Phytocannabinoids bind to the hydrophobic core of the Kv7.4 to augment function. (3) Estradiol-analogue hormones bind to the hydrophobic core of the Kv7.1/E1 channel to inhibit function. Finally, (4) cholesterol binds to the inter-subunit interface of Kv7.5 less stably than within other isoforms to drive unique inhibitory responses.
However, the leveraging of these findings towards novel drug development i.e. a transitioning from subtype- to channelopathy-specificity requires the piecewise answering of multiple questions. Firstly, the molecular mechanisms of channelopathy needs to be elucidated. Secondly, the structural mechanism underlying the ligand’s functional modulation of channel function needs to be deciphered. Finally, ligand chemical features that guide binding and their cross-interaction with channelopathy-inducing mutations need to be identified.
The project aims to answer these questions for each of the four above mentioned molecular scaffolds by compiling a library of atomistic Molecular Dynamics (MD) simulations of Wild-type (WT) and mutant Kv7 ion channels in apo and holo states. Through this, interplay between modulatory drugs and residue mutations can be better understood to help drive the development of Kv7 channelopathy-specific pharmaceutical interventions.