The opening, closing and desensitization of ion channels permit the flow of Sodium (Na+), Calcium (Ca2+) and Potassium (K+) ions across the cell membrane to effectuate the cardiac action potential. Altered activity of any of these ion channels can affect the required synergistic functioning and can give rise to cardiac arrhythmias. The Long QT syndrome (LQTS) is a particularly serious heritable cardiac disorder affecting up to 1 in 2000 people worldwide with a 23-38% risk of death. One of the most common causes of LQTS are the loss of function mutations within the Kv7.1 voltage-gated potassium channel that couples the K+ ion efflux to membrane depolarization. Despite the prevalence of LQTS and its debilitating effects, no approved pharmaceutical intervention exists for both the disease and its causal Kv7.1 ion channel. However, exciting preliminary experimental results from the laboratory have identified estradiol – a steroidal hormone capable of binding and mediating function of the Kv7.1 channel in its cardiac form. In this project, we aim to undertake a series of computational Molecular Dynamics simulations to rationalize the experimental results and thereby lay the stepping-stone for the development of more targeted drugs.
Structurally, the Kv7.1 is a tetrameric potassium channel 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, within cardiac cells, the ion channel functions in combination with KCNE1 – a transmembrane auxiliary protein and phosphatidylinositol-bisphosphate (PIP2) – an anionic lipid predominantly located within the inner leaflet of the bilayer. The KCNE1 auxiliary subunit is crucial in altering the characteristics of the Kv7.1 channel towards its unique role within cardiac cells. Conversely, PIP2 is an essential lipid necessary for channel function and its absence decouples the VSD and PD motions from each other. A lack of molecular mechanisms for the interplay of these important biomolecular counterparts with the Kv7.1 channel is a crucial impediment to drug development. Despite significant efforts and developments in electron microscopy techniques, no structure of the Kv7.1-KCNE1 complex has yet been resolved. Additionally, lipids are notoriously difficult to resolve in structural studies.
Deciphering this complex interplay of the biomolecular triumvirate is further challenged by post-translational modifications. The KCNE1 auxiliary subunit possesses multiple phosphorylation sites within its intracellular disordered regions that can interact with Kv7.1 while simultaneously also disrupt PIP2 binding. Thus, answering this overarching question of cardiac potassium channel druggability requires the piecewise tackling of multiple questions involving its function.
In this project, we aim to address this issue by firstly identifying the cross-interaction profile of Kv7.1, KCNE1, PIP2 and phosphorylation sites. Subsequently, we try to identify the binding site of the experimentally identified modulator estradiol to the biomolecular complex. Finally, we identify plausible residue mutagenesis to experimentally validate the computational predictions.