Biology subjects

Angsutararux, P.

Publications and source records attributed to Angsutararux, P..

4 recordsLinked to original sources

bioRxiv2026

Calcium interaction with Nav1.5 via FGF12A and CaM binding

Voltage-gated Na+ (Nav) channels, including Nav1.5, are responsible for the initiation of cardiac and neuronal action potentials. Regulation of Nav1.5 inactivation is linked to multiple accessory proteins that bind its C-terminal domain (CTD) including calmodulin (CaM) and intracellular fibroblast growth factors (iFGF). Previous results demonstrate that Ca2+-bound CaM preferentially binds to iFGF12A. The role of intracellular Ca2+ ([Ca2+]i) in regulating Nav1.5 gating, either directly or via auxiliary proteins like CaM, is controversial. We hypothesize that CaM binding to the Nav1.5 CTD and iFGF12A synergistically alters channel inactivation in a previously unobserved calcium-dependent manner. We performed Fluorescence Resonance Energy Transfer (FRET) imaging in live cells to observe the interaction between the Nav1.5 alpha subunit, CaM and iFGF12A. At resting [Ca2+]i, a 2-fold difference between acceptor and donor FRET efficiency was observed, implying that a single CaM acceptor is present on the Nav1.5 CTD even in the presence of FGF12A. After increasing [Ca2+]i, the donor and acceptor FRET efficiencies equalize, suggesting a 2:1:1 ratio between CaM, FGF12A, and the Nav1.5 CTD. We then compared the voltage-dependent gating kinetics of Nav1.5 with FGF12A in the presence/absence of calcium. With low [Ca2+]i, the steady-state inactivation of Nav1.5 with FGF12A was significantly shifted toward hyperpolarized potential compared to resting [Ca2+]i. Thus, the FGF12A:CaM complex confers a Ca2+-dependent mechanism enabling FGF12A modulates the Nav1.5 steady-state inactivation. Additionally, the ability of multiple subunits to bring CaM to the Nav1.5 CTD implies biological redundancy to prevent major alteration to Nav1.5 inactivation in the absence of CaM.

biophysics↗

bioRxiv2025

FGF12A Regulates Nav1.5 via CaM-regulated and CaM-independent Mechanisms

Opening of the cardiac voltage-gated Na+ channel (Nav1.5) is responsible for robust depolarization of the cardiac action potential, while inactivation, which rapidly follows, allows for repolarization. Regulation of both the voltage- and time-dependent kinetics of Nav1.5 inactivation can alter the ability of the heart to initiate and sustain a re-entrant arrhythmia. The C-terminal domain (CTD) of Nav1.5 has been shown to modulate fast inactivation of the channel, and multiple auxiliary proteins bind to the CTD, including calmodulin (CaM) and intracellular fibroblast growth factor 12A (FGF12A). Recently, a non-canonical CaM-binding site was also discovered on the N-terminal of A-splice variants of iFGFs. We performed cut-open Vaseline gap (COVG) voltage-clamp to test whether FGF12A with and without CaM regulates Nav1.5 gating. In WT Nav1.5 channels, FGF12A with and without CaM present had a minimal effect on the voltage dependence of both activation and inactivation. Conversely, when CaM is absent on the Nav1.5 CTD (IQ/AA), a dramatic shift in steady-state inactivation (SSI) occurred, regardless of whether CaM was present on FGF12A. These two distinct mechanisms are operative in Nav1.5 LQT3 mutations where FGF12A requires CaM to shift in the voltage-dependence of inactivation, but not to inhibit the persistent late current. We conclude that there are two distinct mechanisms by which FGF12A modulates the Nav1.5 channel: CaM-regulated alteration of the voltage dependence of inactivation and CaM-independent inhibition of persistent late current.

biophysics↗

bioRxiv2023

Arrhythmia-associated Calmodulin Variants Interact with KCNQ1 to Confer Aberrant Membrane Trafficking and Function

RationaleMissense variants in calmodulin (CaM) predispose patients to arrhythmias associated with high mortality rates. As CaM regulates several key cardiac ion channels, a mechanistic understanding of CaM variant-associated arrhythmias requires elucidating individual CaM variant effect on distinct channels. One key CaM regulatory target is the KCNQ1 (KV7.1) voltage-gated potassium channel that underlie the IKs current. Yet, relatively little is known as to how CaM variants interact with KCNQ1 or affect its function. ObjectiveTo observe how arrhythmia-associated CaM variants affect binding to KCNQ1, channel membrane trafficking, and KCNQ1 function. Methods and ResultsWe combine a live-cell FRET binding assay, fluorescence trafficking assay, and functional electrophysiology to characterize >10 arrhythmia-associated CaM variants effect on KCNQ1. We identify one variant (G114W) that exhibits severely weakened binding to KCNQ1 but find that most other CaM variants interact with similar binding affinity to KCNQ1 when compared to CaM wild-type over physiological Ca2+ ranges. We further identify several CaM variants that affect KCNQ1 and IKs membrane trafficking and/or baseline current activation kinetics, thereby contextualizing KCNQ1 dysfunction in calmodulinopathy. Lastly, we delineate CaM variants with no effect on KCNQ1 function. ConclusionsThis study provides comprehensive functional data that reveal how CaM variants contribute to creating a pro-arrhythmic substrate by causing abnormal KCNQ1 membrane trafficking and current conduction. We find that CaM variant regulation of KCNQ1 is not uniform with effects varying from benign to significant loss of function. This study provides a new approach to collecting details of CaM binding that are key for understanding how CaM variants predispose patients to arrhythmia via the dysregulation of multiple cardiac ion channels.

biophysics↗

bioRxiv2020

Mechanical dysfunction induced by a hypertrophic cardiomyopathy mutation is the primary driver of cellular adaptation

Familial hypertrophic cardiomyopathy (HCM), a leading cause of sudden cardiac death, is primarily caused by mutations in sarcomeric proteins. The pathogenesis of HCM is complex, with functional changes that span scales from molecules to tissues. This makes it challenging to deconvolve the biophysical molecular defect that drives the disease pathogenesis from downstream changes in cellular function. Here, we examined a HCM mutation in troponin T, R92Q. We demonstrate that the primary molecular insult driving the disease pathogenesis is mutation-induced alterations in tropomyosin positioning, which causes increased molecular and cellular force generation during calcium-based activation. We demonstrate computationally that these increases in force are direct consequences of the initial molecular insult. This altered cellular contractility causes downstream alterations in gene expression, calcium handling, and electrophysiology. Taken together, our results demonstrate that molecularly driven changes in mechanical tension drive the early disease pathogenesis, leading to activation of adaptive mechanobiological signaling pathways.

biophysics↗