Structural basis of human α7 nicotinic acetylcholine receptor activation

Nicotinic acetylcholine receptors (nAChRs) are a class of pentameric ligand-gated ion channels (pLGICs) widely expressed in nervous system. nAChRs function as neurotransmitter receptors that respond to endogenous acetylcholine and choline, modulating neuronal excitability and synaptic communication. The homomeric α7 nAChR is among the most abundant subtypes of nAChR in the brain. Dysfunction of α7 is found to be associated with several neuropsychiatric and neurologic disorders, including schizophrenia and Alzheimer’s disease. 1 , 2 Stimulation of α7 has been reported to improve attention, cognitive performance, and neuronal resistance to injury. Therefore, agonists and positive allosteric modulators (PAMs) of α7 have become hot candidates in the drug development for the treatment of α7-related diseases. 3 , 4 EVP-6124 (abbreviated as EVP) is a high-affinity α7-selective agonist. 5 PNU-120596 (abbreviated as PNU) is the first reported α7-selective PAM that could increase the peak current of the receptor evoked by agonists and delay channel desensitization. 6 Both EVP and PNU are in clinical trials for the treatment of Alzheimer’s disease, schizophrenia, and cognitive impairment. Despite the significance of α7 in physiology and pharmacology, the mechanisms underlying the activation of α7 upon agonist and/or PAM binding remain elusive. Little is known about the structural basis of the higher selectivity of EVP and PNU for α7, which would be highly valuable for rational drug development targeting the receptor. Herein, we report the structures of full-length human α7 in apo, EVP-bound and EVP/PNU-bound states at 3.18, 2.85 and 3.02 Å, respectively (Fig. 1a–c ; Supplementary information, Figs. S 1 –S 4 and Table S1 ). Fig. 1: Cryo-EM structures of human α7 nicotinic receptor in different states. a – c Cryo-EM maps of human α7 in apo ( a ), EVP-bound ( b ) and EVP/PNU-bound ( c ) states. Chemical structures of EVP and PNU are shown. Representative responses of α7 are shown for the application of 20 µM EVP ( b ), and pre-application of 10 µM PNU followed by 20 µM EVP ( c ). d Overview of the binding sites for EVP from the extracellular space. EVPs are shown as spheres. e Molecular details of the EVP-binding interface viewed from the extracellular space (left) and parallel to the membrane plane (right). EVP is shown as sticks with corresponding density. f Conformational changes in the ligand-binding pocket. Structures of apo-form and EVP-bound α7 are represented as yellow and green ribbons, respectively. g Overview of the binding sites for PNU. PNU is shown as spheres. h Molecular details of the PNU-binding interface viewed parallel to the membrane plane (left) and from the extracellular space (right). PNU is shown as sticks with corresponding density. i Conformational changes in the PNU-binding pocket are shown from the extracellular space. Structures of EVP-bound and EVP/PNU-bound α7 are represented as green and pink ribbons, respectively. Densities for L270 in both the α7/EVP and α7/EVP/PNU models are shown. j Two M2 helices are shown for each of the conformational states. Side chains of pore-lining residues are shown. The channel pore radius was calculated using the HOLE program (red < 1.5 Å ≤ green ≤ 3.0 Å < blue). k Plots of pore radius for α7 in different states along the pore axis. The α-carbon position of 0′ Lys (Lys261) is set to zero. l Comparisons between apo (yellow) and EVP-bound α7 (green) (left), EVP-bound (green) and EVP/PNU-bound α7 (pink) (right), viewed from the extracellular space. Side chains of L270 are shown in ball and stick representation. Full size image