Quantifying the interaction of the C-terminal regions of polycystin-2 and polycystin-1 attached to a lipid bilayer by means of QCM.

The pkd1 and pkd2 genes encode for the proteins polycystin-1 (PC1) and polycystin-2 (PC2). These genes are mutated in patients diagnosed with autosomal dominant polycystic kidney disease. PC1 and PC2 interact via their C-terminal, cytosolic regions, which is an essential step in the regulation of cell proliferation and differentiation. Here, we developed an assay that allowed us to quantitatively monitor the interaction of the C-terminal region of PC1 (cPC1) with that of PC2 (cPC2) to be able to answer the question of how Ca(2+) influences the PC1/PC2 complex formation. By means of the quartz crystal microbalance (QCM) technique, we were able to determine binding affinities and kinetic constants of the cPC1/cPC2 interaction using a model based on the scaled particle theory. The results suggest that cPC2 forms trimers in solution in the absence of Ca(2+), which bind in a one step process to cPC1.