Silva, J. R. | Search bioRxiv

bioRxiv2020

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

Calmodulin (CaM) and PIP2 are potent regulators of the voltage-gated potassium channel KCNQ1 (KV7.1), which conducts the IKs current important for repolarization of cardiac action potentials. Although cryo-EM structures revealed intricate interactions between the KCNQ1 voltage-sensing domain (VSD), CaM, and PIP2, 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 PIP2 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 PIP2 and CaM in KCNQ1 voltage-dependent activation, yielding insights into how KCNQ1 gains the phenotypes critical for its function in the heart.Competing Interest StatementJ.S. and J.C. are cofounders of a startup company VivoCor LLC, which is targeting IKs for the treatment of cardiac arrhythmia. The authors declare that they have no other competing interests.View Full Text

biophysics↗

bioRxiv2020

Proteomic and functional mapping of cardiac NaV1.5 channel phosphorylation reveals multisite regulation of surface expression and gating

Phosphorylation of NaV1.5 channels regulates cardiac excitability, yet the phosphorylation sites regulating channel function and the underlying mechanisms remain largely unknown. Using a systematic quantitative phosphoproteomic approach, we analyzed NaV1.5 channel complexes purified from non-failing and failing mouse left ventricles, and we identified 42 phosphorylation sites on NaV1.5. Most sites are clustered, and three of these clusters are highly phosphorylated. Analyses of phosphosilent and phosphomimetic NaV1.5 mutants revealed the roles of three phosphosites in regulating NaV1.5 channel expression and gating. The phosphorylated serines-664 and -667 regulate the voltage-dependence of channel activation in a cumulative manner, whereas phosphorylation of the nearby serine-671, which is increased in failing hearts, decreases cell surface NaV1.5 expression and peak Na+ current. No additional roles could be assigned to the other clusters of phosphosites. Taken together, the results demonstrate that ventricular NaV1.5 is highly phosphorylated, and that the phosphorylation-dependent regulation of NaV1.5-encoded channels is highly complex, site-specific and dynamic. AbbreviationsA, alanine; E, glutamate; HEK-293, Human Embryonic Kidney 293 cells; INa, peak Na+ current; INaL, late Na+ current; IP, immunoprecipitation; mNaVPAN, anti-NaV channel subunit mouse monoclonal antibody; MS, Mass Spectrometry; MS1, mass spectrum of peptide precursors; MS2 or MS/MS, fragmentation mass spectrum of peptides selected in narrow mass range (2 Da) from MS1 scan; NaV, voltage-gated Na+ channel; pS, phosphoserine; pT, phosphothreonine; S, serine; T, threonine; TAC, Transverse Aortic Constriction; TMT, Tandem Mass Tag.

physiology↗