Structural insight into TRPV5 channel function and modulation

Abstract

TRPV5 (transient receptor potential vanilloid) is a unique calcium-selective TRP channel that is essential for calcium homeostasis. TRPV5 and its close homologue TRPV6 do not exhibit thermosensitivity or ligand-dependent activation, unlike other TRPV channels, but are constitutively opened at physiological membrane potentials. Here, we report high resolution electron cryo-microscopy (cryo-EM) structures of truncated and full length TRPV5 in lipid nanodisc, as well as a TRPV5 W583A mutant structure and a complex structure of TRPV5 with calmodulin (CaM). These structures highlight and explain functional differences between the thermosensitive and calcium-selective TRPV channels. An extended S1-S2 linker folds on top of the channel that might shield it from modulation by extracellular factors. Resident lipid densities in the homologous vanilloid pocket are different from those previously found in TRPV1, supporting a comparatively more rigid architecture of TRPV5. A ring of tryptophan residues (W583) at the bottom of the pore coordinates a density and mutation of W583 resultes in opening of the lower gate. Moreover, we provide structural insight into the calcium-dependent channel inactivation and propose a flexible stoichiometry for TRPV5 and CaM binding.

TRPV5 in renal tubular calcium handling and its potential relevance for nephrolithiasis

“…84 In line with other TRPV structures, the ion permeation pathway also contains a constriction point at the bottom of the pore, referred to as the lower gate. 79,80,83 The significance of a lower gate for TRPV5 channel gating (opening/closing) was proposed previously by our group. 85 Mutations of a tryptophan (W583), uniquely located at the bottom pore of TRPV5 (and TRPV6) and not conserved in other TRPV channels, were shown to result in gain-of-function of TRPV5.…”

“…High-resolution structures of all TRPV channels have been resolved by several independent groups. [74][75][76][77][78][79][80][81] All TRPV channels share a similar tetrameric build, with 6 transmembrane segments (S1-S6) in each segment and large intracellular amino-and carboxy-termini (Figure 2a 82 ). In addition, they have a characteristic amino-terminal ankyrin repeat domain and a highly conserved TRP domain.…”

“…The structure of TRPV5 effectively highlights the selectivity filter at the extracellular side of the pore. 79,80,83 The side chains of the D542 residue form the main constriction point, which is important for Ca 2þ selectivity. 84 In line with other TRPV structures, the ion permeation pathway also contains a constriction point at the bottom of the pore, referred to as the lower gate.…”

“…85 The recent structure of a TRPV5 W583A mutant channel indeed demonstrated an open conformation of the lower gate. 80 Additionally, TRPV5 structures were resolved in complex with CaM. 80,83 CaM is a universal Ca 2þ -sensing protein consisting of 2 lobes (an N and C lobe), each of which contains 2 EF-hand motifs that can bind a Ca 2þ ion.…”

“…80 Additionally, TRPV5 structures were resolved in complex with CaM. 80,83 CaM is a universal Ca 2þ -sensing protein consisting of 2 lobes (an N and C lobe), each of which contains 2 EF-hand motifs that can bind a Ca 2þ ion. Hence, CaM has a total of 4 Ca 2þ -binding sites.…”