Cytoplasmic tail of the putative polycystin channel Pkd2 regulates its clustering in the fission yeast eisosomes

Abstract Polycystins are a family of conserved ion channels, mutations of which lead to human genetic disorder Autosomal Dominant Polycystic Kidney Disease. The unicellular model organism fission yeast Schizosacchromyces pombe possesses single essential polycystin Pkd2 that localizes to the plasma membrane and is required for cell proliferation. Here, we carried out a functional analysis of Pkd2 based on its Alphafold predicted structure. It consisted of N-terminal lipid-binding (LBD), central transmembrane (TMD) and C-terminal cytoplasmic (CCD) domains. LBD assumes a unique immunoglobulin-fold, while TMD contains nine transmembrane helices. Both were essential. Although the mostly disordered CCD was not, its removal led to clustering of Pkd2 in eisosomes, a microdomain of the plasma membrane. Inhibiting eisosome assembly prevented the clustering but disrupting ER-PM contacts further increased it. Pkd2 shared similar structure with two other putative channels Trp663 and Trp1322, but their intracellular localization and function diverged from each other. Replacing LBD with that of Trp663 partially restored the function of Pkd2, but TMD could not be replaced by either that of Trp663 or human polycystins. We concluded that both the plasma membrane microdomains and cytoplasmic tail of Pkd2 regulate the cell surface clustering of this putative ion channel.