X-ray structure of the human α4β2 nicotinic receptor

Abstract

Nicotinic acetylcholine receptors are ligand gated ion channels that mediate fast chemical neurotransmission at the neuromuscular junction and play diverse signaling roles in the central nervous system. The nicotinic receptor has been a model system for cell surface receptors, and specifically for ligand-gated ion channels, for well over a century1,2. In addition to the receptors’ prominent roles in the development of the fields of pharmacology and neurobiology, nicotinic receptors are important therapeutic targets for neuromuscular disease, addiction, epilepsy, and for neuromuscular blocking agents used during surgery2–4. The overall architecture of the receptor was described in landmark studies of the nicotinic receptor isolated from the electric organ of Torpedo marmorata5. Structures of a soluble ligand binding domain have provided atomic-scale insights into receptor-ligand interactions6, while high-resolution structures of other members of the pentameric receptor superfamily provide touchstones for an emerging allosteric gating mechanism7. All available high-resolution structures are of homopentameric receptors. However, the vast majority of pentameric receptors (called Cys-loop receptors in eukaryotes) present physiologically are heteromeric. Here we present the X-ray crystallographic structure of the human α4β2 nicotinic receptor, the most abundant nicotinic subtype in the brain. This structure provides insights into the architectural principles governing ligand recognition, heteromer assembly, ion permeation and desensitization in this prototypical receptor class.

Role of the Cys Loop and Transmembrane Domain in the Allosteric Modulation of α4β2 Nicotinic Acetylcholine Receptors

“…Note that during revision of this manuscript, the X-ray structure of the (␣4␤2) 2 ␤2 nAChR in a presumed desensitized conformation was published (28). We overlaid our homology model and the X-ray structure of the (␣4␤2) 2 ␤2 receptors.…”

“…Moreover, we compared the sensitivity of (␣4␤2) 2 ␤2 and (␣4␤2) 2 ␣4 nAChRs to ACh, Zn 2ϩ , dFBr, and ␤EST using Ringer solutions buffered by HEPES or phosphate buffer and found no differences (not shown). In accord with these findings, the recently published X-ray structure of the (␣4␤2) 2 ␤2 nAChRs suggests that ligands may not access the ␤2/␤2 interface easily (28). Current responses were obtained by two-electrode voltage-clamp recording at a holding potential of Ϫ60 mV using an oocyte clamp OC-725C amplifier (Warner Instruments) and Labscribe software (iWorx, Dover, NH).…”

“…Interactions between post-M4 and Cys Loop Are Necessary for dFBr Potentiation-The atomic structure of post-M4 in pLGICs has not been resolved (3,28). However, because it has been proposed that post-M4 in muscle nAChRs may interact with the Cys loop to modulate gating (8), we hypothesized that post-M4 extends toward the Cys loop and that binding of dFBr to the M3-M4 cavity promotes interactions between Phe 170 and Ile 626 (Fig.…”

Modes of Action, Resistance and Toxicity of Insecticides Targeting Nicotinic Acetylcholine Receptors

“…In pentameric nAChR receptors consisting of 2x α and 3x non-α subunits, the 6 ACh binding site loops (loops A, B and C on the α subunit and loops D, E and F on the non-α subunit) make up the neurotransmitter (orthosteric) binding site, which is located at the α/non-α subunit interfaces. Important roles for loops B C D E and F in interactions with imidacloprid have been reported [25]. Recently, an additional site (loop G) on the β1 strand has been identified [29].…”

“…1). Another recent development has been the successful crystallization of the human α4β2 brain nAChR at 3.9 Angstroms resolution [25].…”