ADPKD Variants in the PKD2 Pore Helix Cause Structural Collapse of the Gate and Distinct Forms of Channel Dysfunction.

PKD2 is a member of the polycystin subfamily of transient receptor potential (TRP) ion channel subunits which traffic and function in primary cilia organelle membranes. Millions of individuals carry pathogenic genetic variants in PKD2 that cause a life-threatening condition called autosomal dominant polycystic kidney disease (ADPKD). Although ADPKD is a common monogenetic disorder, there is no drug cure or available therapeutics which address the underlying channel dysregulation. Furthermore, the structural and mechanistic impact of most disease-causing variants are uncharacterized. Using direct cilia electrophysiology, cryogenic electron microscopy (cryo-EM), and super resolution imaging, we have discovered mechanistic differences in channel dysregulation caused by three germline missense variants located in PKD2's pore helix 1. Variant C632R reduces protein thermal stability, resulting in impaired channel assembly and abolishes primary cilia trafficking. In contrast, variants F629S and R638C retain native cilia trafficking, but exhibit gating defects. Resolved cryo-EM structures (2.7-3.2Å) of the variants indicate loss of critical pore helix interactions and precipitate allosteric collapse of the channels inner gate. Results demonstrate how ADPKD-causing these mutations have divergent and ranging impacts on PKD2 function, despite their shared structural proximity. These unexpected findings underscore the need for mechanistic characterization of polycystin variants, which may guide rational drug development of ADPKD therapeutics. Regarding polycystin nomenclature:The revised and current IUPHAR/BPS nomenclature creates ambiguity regarding the genetic identity of the polycystin family members of transient receptor potential ion channels (TRPP), especially when cross-referencing manuscripts that describe subunits using the former system 1 . Traditionally, the products of polycystin genes (e.g., PKD2) are referred to as polycystin proteins (e.g., polycystin-2). For simplicity and to prevent confusion, we will refer to the polycystin gene name rather than differentiating gene and protein with separate names- a nomenclature we have recently outlined (Annual Reviews in Physiology, Esarte Palomero et al. 2023) 2.