Mechanisms of Tethered-Ligand Mediated Polycystin-1 GPCR Signaling

Abstract

Polycystin-1 (PC1) is the protein product of the most commonly mutated gene in autosomal dominant polycystic kidney disease (ADPKD). PC1 functions as an atypical G protein-coupled receptor (GPCR) and is a subunit of the PC1-PC2 ion channel complex. In vivo studies using different models of ADPKD demonstrated that PC1-regulated G protein signaling is a critical function for preventing renal cystogenesis. ADPKD resulting from non-truncating mutations of PC1 may be amenable to mutation-specific therapies. However, this type of therapeutic approach will not be feasible without an in-depth understanding of the functional mechanisms of PC1. In this study, we have combined functional-biochemical analyses, mutation experiments and accelerated molecular simulations to investigate the dynamic mechanisms of PC1 signaling. All-atom simulations using a robust Gaussian accelerated molecular dynamics (GaMD) method are consistent with mutation experimental data on the PC1 C-terminal fragment (CTF) for the wildtype, ADPKD mutants and CTF without the stalk region (∆CTF). The stalk region is identified to be an important tethered ligand, which mediates PC1-G protein signaling. Key residue interactions predicted from the GaMD simulations are further validated with newly designed mutation experiments. Complementary experiments and simulations have provided important insights into the mechanisms of PC1 GPCR signaling at an atomic level. This is expected to facilitate future drug design efforts targeting PC1 for more effective treatments of ADPKD.