Structural Insights on TRPV5 Gating by Endogenous Modulators

Abstract

TRPV5 is a transient receptor potential channel involved in the vital process of calcium homeostasis, specifically at the level of calcium reabsorption in the kidney. TRPV5 is a constitutively open channel and numerous endogenous modulators tightly regulate calcium entry through the TRPV5 channel into the cell. Here we used cryo-electron microscopy (cryo-EM) to investigate the interaction of two such modulators with full-length TRPV5. Both phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and calmodulin (CaM) have been reported to directly bind to TRPV5 and activate or inactivate the channel, respectively. Using cryo-EM, we have determined the TRPV5 structure in the presence of dioctanoyl PI(4,5)P2, which revealed the key role annular lipids play in maintaining the channel in a conducting state and highlighted the possibility of a transient interaction between dioctanoyl PI(4,5)P2 and the channel. Additionally, we have uncovered the mechanism of TRPV5 calcium-dependent inactivation, which is mediated by the binding of one CaM molecule per TRPV5 tetramer. This novel mechanism involves the C-lobe of calcium activated CaM physically obscuring the ion conducting pore of TRPV5 by binding to critical tryptophan residues (Trp583) at the intracellular gate of TRPV5. This interaction is initiated by the binding of the CaM C-lobe to the distal C-terminus of TRPV5 which brings CaM in close proximity to the TRPV5 pore. Overall, this investigation has provided insight into the endogenous modulation of TRPV5 which has the potential to guide in silico drug discovery and rational drug design for targeted therapeutics for a variety of calcium dependent kidney diseases.