Cryo-EM structure of the human histamine H1 receptor/Gq complex

Ruixue Xia,Changyou Guo,Na Wang,Yang Lu,Anqi Zhang,Yuanzheng He,Zhenmei Xu,Jing Song

doi:10.1038/s41467-021-22427-2

Abstract

Histamine receptors play important roles in various pathophysiological conditions and are effective targets for anti-allergy treatment, however the mechanism of receptor activation remain elusive. Here, we present the cryo-electron microscopy (cryo-EM) structure of the human H1R in complex with a Gq protein in an active conformation via a NanoBiT tethering strategy. The structure reveals that histamine activates receptor via interacting with the key residues of both transmembrane domain 3 (TM3) and TM6 to squash the binding pocket on the extracellular side and to open the cavity on the intracellular side for Gq engagement in a model of “squash to activate and expand to deactivate”. The structure also reveals features for Gq coupling, including the interaction between intracellular loop 2 (ICL2) and the αN-β junction of Gq/11 protein. The detailed analysis of our structure will provide a framework for understanding G-protein coupling selectivity and clues for designing novel antihistamines.

Highlights

Histamine receptors play important roles in various pathophysiological conditions and are effective targets for anti-allergy treatment, the mechanism of receptor activation remain elusive
To facilitate the cryoEM structure solving, we use an engineered Gq protein (GqiN) in which the N-terminus of Gq was replaced by the N-terminus of Gi protein to render the protein binding ability to the scFv16 antibody that has been successfully used in solving numerous receptor/G-protein complexes[16,18,19,20], including the M1R/G11 complex
The NanoBiT tethering strategy greatly improves the composition of the complex (Supplementary Fig. 3), and the structure was solved by the single-particle cryo-electron microscopy (cryo-EM) analysis of the H1R-large part of NanoBiT (LgBiT)/GαqiN/Gβ-HiBiT/Gγ/scFv16 complex at 3.64 Å resolution (Methods and Supplementary Figs. 4–6)

Summary

Introduction

Histamine receptors play important roles in various pathophysiological conditions and are effective targets for anti-allergy treatment, the mechanism of receptor activation remain elusive. 1234567890():,; Histamine is a biogenic amine that mediates a variety of pathophysiological responses and signaling events through the binding of histamine receptors, members of the class A G-protein-coupled receptor (GPCR) superfamily[1]. Histamine binding of receptor recruits heterotrimeric G-protein and triggers downstream signaling cascade. An early study has revealed the structure of H1R bound to the first generation of antihistamine, doxepin, in an inactive conformation[10]. The muscarinic acetylcholine receptor 1 (M1R)/G11 complex structure first revealed some distinct features for the Gq/ 11-coupled receptors, including an extended TM5 and a receptor c-tail/G-protein interaction[16]. It is imaginable that with more Gq-coupled receptor complex structures being solved, a pattern of receptor/Gq engagement can be found

Methods

Results

Conclusion