The proteostasis interactomes of trafficking-deficient variants of the voltage-gated potassium channel K_V11.1 associated with long QT syndrome

The voltage-gated potassium ion channel K_V11.1 plays a critical role in cardiac repolarization. Genetic variants that render Kv11.1 dysfunctional cause long QT syndrome (LQTS), which is associated with fatal arrhythmias. Approximately 90% of LQTS-associated variants cause intracellular protein transport (trafficking) dysfunction, which pharmacological chaperones like E-4031 can rescue. Protein folding and trafficking decisions are regulated by chaperones, protein quality control factors, and trafficking machinery comprising the cellular proteostasis network. Here, we test whether trafficking dysfunction is associated with alterations in the proteostasis network of pathogenic Kv11.1 variants and whether pharmacological chaperones can normalize the proteostasis network of responsive variants. We used affinity-purification coupled with tandem mass tag-based quantitative mass spectrometry to assess protein interaction changes of WT K_V11.1 or trafficking-deficient channel variants in the presence or absence of E-4031. We identified 572 core K_V11.1 protein interactors. Trafficking-deficient variants K_V11.1-G601S and K_V11.1-G601S-G965^∗ had significantly increased interactions with proteins responsible for folding, trafficking, and degradation compared to WT. We confirmed previous findings that the proteasome is critical for K_V11.1 degradation. Our report provides the first comprehensive characterization of protein quality control mechanisms of K_V11.1. We find extensive interactome remodeling associated with trafficking-deficient K_V11.1 variants and with pharmacological chaperone rescue of K_V11.1 cell surface expression. The identified protein interactions could be targeted therapeutically to improve K_V11.1 trafficking and treat LQTS.