SUMOylation and an ATS1 variant converge to disrupt PIP₂-dependent gating of Kir2.1

Precise control of Kir2.1 channel gating is essential for maintaining membrane potential and enabling repolarization in excitable cells. Disruption of Kir2.1 function can cause Andersen-Tawil syndrome type 1 (ATS1), a multisystem channelopathy that predisposes patients to ventricular dysrhythmias and increases the risk of sudden cardiac death. Kir2.1 activity depends on interactions with the membrane phospholipid PIP₂, and these interactions can be weakened by genetic mutations or posttranslational modifications. Here, we identify a shared mechanism by which hypoxia-induced SUMOylation and a heterozygous ATS1-linked variant, R67Q, independently and cooperatively suppress Kir2.1 function. We found that SUMOylation reduces Kir2.1 current in a stoichiometric manner, with up to two SUMO proteins per channel tetramer diminishing current by ∼24% each. Channels containing heterozygous R67Q subunits are disproportionately sensitive to hypoxic suppression. Inhibiting the SUMO pathway with TAK-981 prevents this suppression and enhances current in both WT and R67Q-containing channels. Further analysis revealed that both SUMOylation and the R67Q mutation reduce the stability of Kir2.1–PIP₂ interactions, indicating a convergent gating defect. These findings support a two-hit model of channel dysfunction, in which a genetic variant and an environmental stressor act through a common structural mechanism to impair Kir2.1 gating. By identifying PIP₂ destabilization as the point of convergence, this work provides new insight into how stress-sensitive channelopathies arise and suggests that SUMO pathway inhibition may offer a strategy to restore function under adverse physiological conditions.