Structural basis for Ca2+ activation of the heteromeric PKD1L3/PKD2L1 channel

Qiang Su,Yigong Shi,Xiechao Zhan,Dan Jing,Yan Wang,Yong Yu,Bin Li,Mengying Chen

doi:10.1038/s41467-021-25216-z

Abstract

The heteromeric complex between PKD1L3, a member of the polycystic kidney disease (PKD) protein family, and PKD2L1, also known as TRPP2 or TRPP3, has been a prototype for mechanistic characterization of heterotetrametric TRP-like channels. Here we show that a truncated PKD1L3/PKD2L1 complex with the C-terminal TRP-fold fragment of PKD1L3 retains both Ca2+ and acid-induced channel activities. Cryo-EM structures of this core heterocomplex with or without supplemented Ca2+ were determined at resolutions of 3.1 Å and 3.4 Å, respectively. The heterotetramer, with a pseudo-symmetric TRP architecture of 1:3 stoichiometry, has an asymmetric selectivity filter (SF) guarded by Lys2069 from PKD1L3 and Asp523 from the three PKD2L1 subunits. Ca2+-entrance to the SF vestibule is accompanied by a swing motion of Lys2069 on PKD1L3. The S6 of PKD1L3 is pushed inward by the S4-S5 linker of the nearby PKD2L1 (PKD2L1-III), resulting in an elongated intracellular gate which seals the pore domain. Comparison of the apo and Ca2+-loaded complexes unveils an unprecedented Ca2+ binding site in the extracellular cleft of the voltage-sensing domain (VSD) of PKD2L1-III, but not the other three VSDs. Structure-guided mutagenic studies support this unconventional site to be responsible for Ca2+-induced channel activation through an allosteric mechanism.

Highlights

The heteromeric complex between PKD1L3, a member of the polycystic kidney disease (PKD) protein family, and PKD2L1, known as TRPP2 or TRPP3, has been a prototype for mechanistic characterization of heterotetrametric TRP-like channels
The results show that, similar to that of the FL PKD1L3/PKD2L1 complex, obvious Ca2+ and acid-induced currents were recorded from the PKD1L3-carboxy-terminal domain (CTD)/2L1 complex, suggesting the presence of Ca2+ and pH sensor on this minimal complex (Fig. 1b, c and Supplementary Fig. 2a)
Our results are consistent with a previous report showing the complex formed by the PKD1-CTD and PKD2 resembles the channel function of the full-length complex[37]

Summary

Introduction

The heteromeric complex between PKD1L3, a member of the polycystic kidney disease (PKD) protein family, and PKD2L1, known as TRPP2 or TRPP3, has been a prototype for mechanistic characterization of heterotetrametric TRP-like channels. Comparison of the apo and Ca2+-loaded complexes unveils an unprecedented Ca2+ binding site in the extracellular cleft of the voltage-sensing domain (VSD) of PKD2L1-III, but not the other three VSDs. Structure-guided mutagenic studies support this unconventional site to be responsible for Ca2+-induced channel activation through an allosteric mechanism. The heterotetrameric PKD1L3/2L1 was found in a subset of taste receptor cells that are responsible for acid sensing and suggested to be a sour taste receptor candidate[10,19,23,24,25] This hypothesis has been recently challenged by animal studies and the identification of the Otop[1] proton channel as the primary sour taste receptor[26,27,28,29]. The real role of the PKD1L3/2L1 complex in sour taste needs further investigation

Methods

Results

Conclusion