Anti-Nicotinic Acetylcholine Receptor α1 (CHRNA1) (extracellular) Antibody

Acetylcholine, released by cholinergic neurons, activates two groups of acetylcholine receptors (AChRs); muscarinic AChRs (mAChRs) which belong to the superfamily of G-protein coupled receptors (GPCRs) and nicotinic AChRs (nAChRs) which belong to the ligand-gated ion channel superfamily. nAChRs also respond to nicotine, hence their name¹.

To date, 17 different but related subunits of nAChRs have been identified and cloned. They consist of α subunits (α1-10), which is responsible for the binding of ligands. In fact, this subunit includes a Cys-loop in the first extracellular domain that is required for agonist binding². The other subunits responsible for making up the active receptor are the β (β1-4), γ, δ and ε subunits³. Structurally, all subunits have the following: a conserved large extracellular N-terminal domain, 3 conserved transmembrane domains, a variable cytoplasmic loop and a fourth transmembrane domain with a short extracellular C-terminal domain.  An active nAChR is generally a heteropentamer (homopentamers also exist) of these various subunits organized around a central pore¹.

All α subunits are expressed in neuronal cells except for the α1 subunit which is specifically expressed in skeletal muscle. Indeed, two different nAChR structural entities with the following stoichiometry are observed in this tissue: (α1)₂β1δγ in fetal muscle cells and (α1)₂β1δε at mature neuromuscular synapses³.
The α1 extracellular domain contains the main immunogenic region, a region against which a large fraction of autoantibodies against nAChR is directed in the autoimmune disease myasthenia gravis (MG)⁴. This autoimmune disease is characterized by the malfunction of neuromuscular transmission as a result of nonfunctional nAChRs, leading to defective signaling at the neuromuscular junction⁵.

Due to its central role in muscle contraction and autonomic nervous system, nAChRs have evolved to be important targets of toxins secreted by plants, insects and animals. One prominent toxin affecting α1, in addition to other subunits, is α-bungarotoxin (#B-100), a snake toxin which blocks nAChRs⁶.