Title:	Lipid Modulation of Kv7 Voltage Gated Ion Channels
DNr:	LiU-compute-2022-37
Project Type:	LiU Compute
Principal Investigator:	Sara Liin <sara.liin@liu.se>
Affiliation:	Linköpings universitet
Duration:	2022-12-22 – 2024-01-01
Classification:	10603
Homepage:	https://liu.se/en/employee/sarbo42
Keywords:

Abstract

Ion channels facilitate the ‘electrical signals of life’ by opening, closing and desensitizing to regulate the flow of ions across the cellular membrane. 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 ion channels and are distributed across a range of tissues. The Kv7.1 channel is expressed in cardiomyocytes and is essential for cardiac function. The Kv7.2 and Kv7.3 channels together form heteromers within neurons and control excitability. The Kv7.4 channel is expressed within cochlear hair cells and plays a role in sound amplification. Finally, the Kv7.5 channel regulates excitability within smooth muscles. This ubiquitous distribution of Kv7 channels and roles in a multitude of cellular processes cause their misfunction to be associated with a range of disorders including long-QT syndrome, epilepsy, deafness and loss of bladder control. Despite this prevalence of Kv7-associated disorders, no approved drugs for the channels exists. In fact, the only two approved Kv7 channel openers – Retigabine and Flupirtine were both withdrawn due to undesirable off-target effects. A significant basis for this lack of pharmacotherapic headway is the similarity of the Kv7 channel isoforms. Despite distinct tissue distribution and physiological roles, the five subtypes are incredibly similar in both sequence and structure. The channels are all assemble as tetramers with each subunit composed of four transmembrane helices making up the voltage-sensing domain (VSD) and two helices making up the pore domain (PD). However, exciting preliminary experimental results from the laboratory have identified the subtypes to display differing sensitivity to membrane lipid compositions. The Kv7.4 channel has been identified to be particularly sensitive to cholesterol concentrations. Conversely, the normally insensitive cardiac Kv7.1 channel is positively modulated by cholesterol when long-QT mutations are incorporated. These results allow a fascinating new methodology for drug development – the rationalization of endogenous lipid-protein interactions to design subtype-specific lipid-mimetic drugs. However, deciphering the mechanism of these lipid induced effects is particularly challenging as cholesterol can have both direct and indirect effects. Primarily, the molecule can directly bind and modulate ion channels. Additionally, the molecule also has secondary effects where it can rigidify the membrane to affect curvature and thereby the behaviour of other members of the lipidome. In this project, we aim to utilize computational modelling to rationalize this lipid modulation and to subsequently guide electrophysiology experiments. Towards this, we leverage Alphafold to first build and equilibrate structures of the Kv7.3 and Kv7.5 channels hitherto without cryo-electron microscopy structures. Subsequently, all five members of the family are embedded in coarse-grain (CG) model neuronal membranes. The systematic set of simulations would allow both the differing lipid binding events and membrane curvature/thickness across the subtypes to be deciphered. Finally, to provide plausible residue mutagenesis for experimental validation, the CG lipid-bound configurations are backmapped and modelled in the atomistic resolution.