Functionally Aberrant Mutant KCNQ1 With Intermediate Heterozygous and Homozygous Phenotypes

Area of Science:

• Cardiovascular Physiology
• Molecular Cardiology
• Genetics of Cardiac Arrhythmias

Background:

• Mutations in KCNQ1 cause Long QT Syndrome (LQTS), a disorder linked to ventricular tachyarrhythmias.
• LQTS results from reduced KCNQ1 potassium current (I_Ks), affecting cardiac repolarization.
• This study investigates the KCNQ1-R562S mutation's impact on LQTS.

Purpose of the Study:

• To determine the functional consequences of the KCNQ1-R562S mutation.
• To analyze the mutation's effect on I_Ks current and its association with KCNE1.
• To correlate the mutation's biophysical properties with clinical LQTS phenotypes.

Main Methods:

• Confocal imaging and surface biotinylation to assess protein trafficking.
• Co-immunoprecipitation and pulldown assays to study protein interactions.
• Whole-cell patch clamp electrophysiology to analyze channel function.
• Computational analyses for intrinsic disorder prediction.

Main Results:

• KCNQ1-R562S protein expression, assembly with KCNE1, and surface trafficking were similar to wild-type.
• The R562S mutation caused a depolarizing shift in activation voltage dependence, contingent on KCNE1 association.
• Impaired interaction with phosphatidylinositol-4,5-bisphosphate and compromised rate-dependent current accumulation were observed.

Conclusions:

• KCNQ1-R562S mutation reduces I_Ks via altered channel gating, causing a mild LQTS phenotype in heterozygotes.
• The mutation exhibits a partially dominant negative effect, leading to incomplete I_Ks loss.
• Homozygous KCNQ1-R562S results in a moderately severe LQTS phenotype due to incomplete I_Ks absence.