Structural principles of distinct assemblies of the human α4β2 nicotinic receptor

Abstract

SummaryFast chemical communication in the nervous system is mediated by neurotransmitter-gated ion channels. The prototypical member of this class of cell surface receptors is the cation-selective nicotinic acetylcholine receptor. As with most ligand-gated ion channels, nicotinic receptors assemble as oligomers of subunits, usually as hetero-oligomers and often with variable stoichiometries1. This intrinsic heterogeneity in protein composition provides the fine tunability in channel properties essential to brain function but frustrates structural and biophysical characterization. The α4β2 subtype of the nicotinic acetylcholine receptor is the most abundant isoform in the human brain and is the principal target in nicotine addiction. This pentameric ligand-gated ion channel assembles in two stoichiometries of α and β subunits, 2α:3β and 3α:2β. Both assemblies are functional, have distinct biophysical properties, and a misbalance in the ratio of assemblies is tied to both nicotine addiction2,3 and congenital epilepsy4,5. Here we leverage cryo-electron microscopy (cryo-EM) to obtain structures of both receptor assemblies from a single sample. Antibody fragments specific to β2 were used to ‘break’ symmetry during particle alignment and obtain high resolution reconstructions of both stoichiometries, in complex with nicotine. The results reveal principles of subunit assembly and the structural basis of the distinctive biophysical and pharmacological properties of the two different stoichiometries of this receptor.

Mechanism of gating and partial agonist action in the glycine receptor

“…6g). As a consequence, although the extracellular upper half of the pore has a small movement at 9’L, the intracellular lower half of the pore is occluded at −2’P, moving by ∼1.4 Å, in agreement with observations in the homomeric-GABA A receptor and the α4β2 nicotinic receptor in the desensitized state 46–48 (Fig. 5a, h, j).…”

Inhale, exhale: Probing the inside-out mechanism of nicotine addiction using novel fluorescent sensors

“…The earliest concept of a receptor molecule originated, in part, from studies of effects of nicotine and curare on this synapse (Langley, 1914). The following century or more of work has led to an impressive accumulation of mechanistic understanding, which has largely been driven by preceding technical advances including intracellular recordings (Fatt and Katz, 1951), electron microscopy (De Robertis and Bennett, 1954;Palade and Palay, 1954), voltage clamp recording (Magleby and Stevens, 1972), fluctuation analysis (Katz and Miledi, 1972;Anderson and Stevens, 1973), single channel recording (Neher and Sakmann, 1976) and cryo-EM (Walsh et al, 2018).…”

Chronic Menthol Does Not Change Stoichiometry or Functional Plasma Membrane Levels of Mouse α3β4-Containing Nicotinic Acetylcholine Receptors

“…Furthermore, functional a3b4b3 nAChRs are present in the brain (Grady et al, 2009). It remains possible that the subunit in the accessory position influences the nature of the subunit interfaces (Walsh et al, 2018), and hence potentially the effects from chronic treatments by menthol or other chaperones.…”