Ion channel function of polycystin-2/polycystin-1 heteromer revealed by structure-guided mutagenesis
Autosomal-dominant polycystic kidney disease (ADPKD) is caused by mutations affecting polycystin-1 (PC1) or polycystin-2 (PC2). Recent structural data suggest that PC1 and PC2 can form heterotetrameric ion channels with a 3:1 stoichiometry, with the channel in a closed state. In this hetero-oligomeric formation three PC1 residues (R4100, R4107, and H4111) would work together with two PC2 residues (L677, N681) to block the ion permeation pathway. Here, we provide functional evidence supporting this model. When the pore-blocking residues are replaced by alanines, there is a significant gain-of-function (GOF) effect on PC2/PC1 currents. These PC2/PC1 GOF channels show different selectivity for monovalent cations and reduced Ca2+ permeability compared to PC2 homomers. By varying the expression ratio of PC1 and PC2, we found that PC2 preferentially forms heteromeric complexes with PC1 over homomers. Additionally, a re-interpretation of published PC2/PC1 cryo-electron microscopy data, combined with cysteine modification experiments, suggests that the pore-forming domain of PC1 adopts a canonical TRP-like conformation. The novel PC2/PC1 GOF construct offers a promising approach to investigate the functional impact of mutations linked to ADPKD.