Arrhythmia-associated calmodulin variants interact with KCNQ1 to confer aberrant membrane trafficking and function

Area of Science:

• Biological Sciences
• Health and Medical Sciences
• Physiology

Background:

• Missense variants in calmodulin (CaM) are linked to fatal arrhythmias (calmodulinopathy).
• CaM regulates critical cardiac ion channels, but its variants' specific effects on channels like KCNQ1 are poorly understood.
• Understanding CaM variant impacts on KCNQ1 is crucial for elucidating arrhythmia mechanisms.

Purpose of the Study:

• To investigate how over 10 arrhythmia-associated CaM variants affect KCNQ1 binding, membrane trafficking, and function.
• To determine the impact of CaM variants on KCNQ1 channel activity and the I_Ks current.
• To differentiate CaM variants with varying effects on KCNQ1, from benign to loss-of-function.

Main Methods:

• Live-cell fluorescence resonance energy transfer (FRET) binding assays to measure CaM-KCNQ1 interaction.
• Fluorescence trafficking assays to assess KCNQ1 localization at the cell membrane.
• Functional electrophysiology to analyze KCNQ1 channel activity and I_Ks current.

Main Results:

• One CaM variant (G114W) showed significantly reduced binding to KCNQ1.
• Most CaM variants maintained similar binding affinity to KCNQ1 across physiological calcium ranges.
• Several CaM variants altered KCNQ1 membrane trafficking and/or activation kinetics, impacting I_Ks.
• Some CaM variants had no discernible effect on KCNQ1 function.

Conclusions:

• CaM variants contribute to a proarrhythmic state through aberrant KCNQ1 trafficking and function.
• CaM variant effects on KCNQ1 are heterogeneous, ranging from minimal to significant loss-of-function.
• Dysregulation of KCNQ1 by CaM variants contributes to arrhythmia susceptibility, highlighting channel-specific impacts.