Crystal structure of the extracellular domain of nAChR α1 bound to α-bungarotoxin at 1.94 Å resolution

Abstract

We determined the crystal structure of the extracellular domain of the mouse nicotinic acetylcholine receptor (nAChR) alpha1 subunit bound to alpha-bungarotoxin at 1.94 A resolution. This structure is the first atomic-resolution view of a nAChR subunit extracellular domain, revealing receptor-specific features such as the main immunogenic region (MIR), the signature Cys-loop and the N-linked carbohydrate chain. The toxin binds to the receptor through extensive protein-protein and protein-sugar interactions. To our surprise, the structure showed a well-ordered water molecule and two hydrophilic residues deep in the core of the alpha1 subunit. The two hydrophilic core residues are highly conserved in nAChRs, but correspond to hydrophobic residues in the nonchannel homolog acetylcholine-binding proteins. We carried out site-directed mutagenesis and electrophysiology analyses to assess the functional role of the glycosylation and the hydrophilic core residues. Our structural and functional studies show essential features of the nAChR and provide new insights into the gating mechanism.

Insight in nAChR subtype selectivity from AChBP crystal structures

“…Hence, CLR modeling strategies have heavily relied on the X-ray structures of AChBPs and their complexes together with the structure of the Torpedo nAChR [24][25][26][27]. The availability of the recently solved X-ray structure of the monomeric mouse α 1 nAChR subunit in complex with α-Bungarotoxin [28] indeed illustrates that AChBP constitutes a very good model for studying nAChRs, especially when considering the high degree of structural similarity between the α 1 and AChBP structures; mouse α 1 nAChR subunit superposes to carbamylcholine-bound LsAChBP with an r.m.s. deviation of 1.29Å (Figure 1c) [29].…”

Agonist activation of α7 nicotinic acetylcholine receptors via an allosteric transmembrane site

“…3D structural information is available for individual nAChR subunit domains (9) and for intact nAChRs (10). In addition, high-resolution structural information has been obtained from acetylcholine binding proteins, which share close sequence similarity to the nAChR extracellular region (11).…”

Molecular mechanisms of acetylcholine receptor–lipid interactions: from model membranes to human biology

“…The structural independence of the ABD is supported by the existence of stable pentameric water-soluble acetylcholine binding proteins, which are homologous to the ABD of the nAChR (Brejc et al 2001;Hansen et al 2005). Folded, stable, and water-soluble ABDs of the nAChR α1-and α7-subunits, as well as the prokaryotic homolog, GLIC, can be expressed independently of their TMDs (Dellisanti et al 2007;Nury et al 2010;Li et al 2011).…”

“…In the past decade, a cryo-electron microscopy model of the Torpedo nAChR (Unwin 2005), along with X-ray crystal structures of the homologous prokaryotic pentameric ligandgated ion channels, GLIC and ELIC Dutzler 2008, 2009;Bocquet et al 2009), a glutamate-activated chloride channel (Hibbs and Gouaux 2011), and the water-soluble homologs of the nAChR extra-membranous agonist-binding domain (Dellisanti et al 2007;Brejc et al 2001;Hansen et al 2005;Celie et al 2004;Li et al 2011), have all been published. With these structures, we are now poised to understand functional data on nAChR-lipid interactions in a structural/ mechanistic context.…”