Calmodulin acts as a state-dependent switch to control a cardiac potassium channel opening

Abstract

<jats:title>Abstract</jats:title><jats:p>Calmodulin (CaM) and PIP<jats:sub>2</jats:sub> are potent regulators of the voltage-gated potassium channel KCNQ1 (K<jats:sub>V</jats:sub>7.1), which conducts the I<jats:sub>Ks</jats:sub> current important for repolarization of cardiac action potentials. Although cryo-EM structures revealed intricate interactions between the KCNQ1 voltage-sensing domain (VSD), CaM, and PIP<jats:sub>2</jats:sub>, the functional consequences of these interactions remain unknown. Here, we show that CaM-VSD interactions act as a state-dependent switch to control KCNQ1 pore opening. Combined electrophysiology and molecular dynamics network analysis suggest that VSD transition into the fully-activated state allows PIP<jats:sub>2</jats:sub> to compete with CaM for binding to VSD, leading to the conformational change that alters the VSD-pore coupling. We identify a motif in the KCNQ1 cytosolic domain which works downstream of CaM-VSD interactions to facilitate the conformational change. Our findings suggest a gating mechanism that integrates PIP<jats:sub>2</jats:sub> and CaM in KCNQ1 voltage-dependent activation, yielding insights into how KCNQ1 gains the phenotypes critical for its function in the heart.</jats:p>

Network analysis reveals how lipids and other cofactors influence membrane protein allostery

“…The CTD-bent state allows interactions between CaM and the VSD, which are disrupted in the CTD-straight channel. Recent studies showed that both states are present in the channel activation pathway [21]. to not significantly increase signaling efficiency alone.…”

“…1 shows a flowchart of how the network is built using MD simulation data. We use a continuous contact map and positional mutual information to model spatial proximity and correlation of residue movements, respectively (see details below) [21].…”

“…Continuous contact maps yield more stable networks than binary ones [14]. A switchingfunction, K(d) introduced in [21] is used. Given the minimum distance d i j (n) between atoms of nodes i and j in frame n,…”

“…Correlation of residue and interactor node movements are modeled with positional mutual information (MI) of node centroids [21,28]. This measures correlation of fluctuation distances around an equilibrium position by characterizing the amount of information that can be inferred about a specific node position knowing the position of another node.…”

“…Current flow betweenness was first introduced to biomolecular simulations in the context of a soluble enzyme [14]. A homomeric-averaged variant was recently presented and experimentally validated on KCNQ1 [21]. The current flow betweenness from each subunit was replicated and summed over the structure prior to averaging.…”