Disrupting polycystin-2 EF hand Ca(2+) affinity does not alter channel function or contribute to polycystic kidney disease

Approximately 15% of autosomal dominant polycystic kidney disease (ADPKD) is caused by variants in PKD2. PKD2 encodes polycystin-2, which forms an ion channel in primary cilia and endoplasmic reticulum (ER) membranes of renal collecting duct cells. Elevated internal Ca(2+) modulates polycystin-2 voltage-dependent gating and subsequent desensitization – two biophysical regulatory mechanisms that control its function at physiological membrane potentials. Here, we refute the hypothesis that Ca(2+) occupancy of the polycystin-2 intracellular EF hand is responsible for these forms of channel regulation, and, if disrupted, results in ADPKD. We identify and introduce mutations that attenuate Ca(2+)-EF hand affinity but find channel function is unaltered in the primary cilia and ER membranes. We generated two new mouse strains that harbor distinct mutations that abolish Ca(2+)-EF hand association but do not result in a PKD phenotype. Our findings suggest that additional Ca(2+)-binding sites within polycystin-2 or Ca(2+)-dependent modifiers are responsible for regulating channel activity.