Long QT syndrome-associated calmodulin mutations and their interactions with the Kv7.1 voltage-gated potassium channel

Abstract Introduction Calmodulin (CaM) is a highly conserved mediator of calcium (Ca2+) dependent signalling. Its flexible structure allows CaM to bind and modulate many targets, including cardiac ion channels. Genotyping has revealed several mutations associated with congenital disorders heart rhythm, known as long QT-syndrome (LQTS). LQTS patients suffer from prolonged ventricular recovery times (QT-interval) which increases their risk significant events. Loss function KV7.1 are the largest cause LQTS, accounting for >50% cases. facilitates Ca2+-sensitivity in producing IKs, Kv7.1 reduce binding promote pathology. However, effects LQTS-associated on remain unknown. Purpose To determine biophysical consequences how they alter modulation repolarising IKs current. Methods WT mutant proteins were recombinantly expressed purified characterisation. Using circular dichroism, secondary structures thermostability quantified. Isothermal titration calorimetry was used quantitatively measure interactions between sites (Helix B). NMR employed study conformations target-bound proteins. Whole cell currents determined using voltage clamp electrophysiology HEK cells. Results Mutations significantly changed distributions CaM, also caused site-dependent susceptibility protease digestion. interacted Helix B (KV7.1) via both Ca2+-dependent independent mechanisms. Ca2+ much higher affinity than Ca2+-independent binding, >2000-fold reduction dissociation constant measured. LQTS-CaM variants reduced reductions found EF-hand IV mutants. These mutants adopted most distinct when B-bound. Calmodulation channel produced larger (IKs) without altering activation kinetics. exhibited Ca2+-sensitivity, response increased cytosolic Ca2+, generated. Modulation by current density at systolic Ca2+-concentrations (1000 nM), within physiological time periods (0.35 s), revealing direct QT-prolonging modulatory effect. Conclusions Provided here mechanistic insights contribute electrical disease heart. disrupt protein conformation perturb complex formation KV7.1. This results aberrant Kv7.1, reducing generation. ultimately decreases repolarisation capacity cells would extend QT interval myocytes. Funding Acknowledgement Type funding sources: Foundation. Main source(s): British Heart Foundation Intermediate Basic Science Research Fellowship