Abstract P-7: Cryoelectron Microscopy Study of Water-Soluble Extracellular Domain of α7 Nicotinic Acetylcholine Receptor

• Main Authors: Andrey V. Tsarev, Roman A. Kamyshinsky, Vasiliy I. Mikirtumov, Dmitriy S. Kulbatskii, Eugene O. Yablokov, Zakhar O. Shenkarev, Olga S. Sokolova, Ekaterina N. Lyukmanova
• Format: Article
• Language: English
• Published: International Medical Research and Development Corporation 2019-06-01
• Series: International Journal of Biomedicine
• Subjects: cryo-electron microscopy; α7-nAChR; beta-amyloid peptide
• Online Access: http://ijbm.org/articles/IJBM_2019_9_S1_P7.pdf

Background: Nicotinic acetylcholine receptor (nAChR) is a ligand-gated ion channel, which is widely distributed both in the central and peripheral nervous system, and in some of the non-neuronal tissues, including epithelium and immune cells. The pathophysiology of a number of diseases is associated with dysfunctions of this receptor, including neurodegenerative and mental disorders like Alzheimer disease (AD) and schizophrenia. The nicotinic receptor of α7 type (α7-nAChR) plays important role in the memory and learning processes and is inhibited by soluble aggregates of β-amyloid peptide (Aβ). Aβ1-42 is the most toxic form of the amyloid peptide. Methods: The water-soluble analogue of the ligand-binding extracellular domain of α7-nAChR was produced in Pichia pastoris and purified from a culture medium by Ni-NTA and size-exclusion chromatography. The equilibrium dissociation constant (Kd) of the complex of the recombinant domain with α-bungarotoxin was measured on the optical SPR biosensor Biacore 3000. Structures of the α7 domain alone and in the complex with oligomeric Aβ1-42 peptide were studied by cryoelectron microscopy (cryo-EM). Results: The α7 ligand-binding domain has an increased stability in solution, and demonstrates ligand-binding characteristics similar to those of the native receptor (Kd of the domain/α-bungarotoxin complex 28±2nM). Statistical analysis of the cryo-EM images of the individual domain particles revealed the presence of a pentameric structure, confirming intact subunit assembly. Unfortunately, the domain demonstrated the preferable orientation on grids with the top view. Nevertheless, the 3D structure of the domain with a height ~ 7 nm, external diameter of ~ 9 nm, and the pore diameter of ~ 2 nm was reconstructed at 8.5 Å resolution. 2D classification of the cryo-EM images of the domain particles in the complex with Aβ1-42 revealed the conformational changes appeared due to interaction with the amyloid peptide. Conclusion: Obtained results open new perspectives for structural studies of the nAChR ligand-binding domains in complex with the ligands which escape crystallization.