page_title: Nicotinic acetylcholine receptor
section_title: Structure
hierarchical_section_title: Nicotinic acetylcholine receptor / Structure
caption_attribution_description: English: nicotinic acetylcholine receptor
context_page_description: Nicotinic acetylcholine receptors, or nAChRs, are receptor polypeptides that respond to the neurotransmitter acetylcholine. Nicotinic receptors also respond to drugs such as the agonist nicotine. They are found in the central and peripheral nervous system, muscle, and many other tissues of many organisms. At the neuromuscular junction they are the primary receptor in muscle for motor nerve-muscle communication that controls muscle contraction. In the peripheral nervous system: they transmit outgoing signals from the presynaptic to the postsynaptic cells within the sympathetic and parasympathetic nervous system, and they are the receptors found on skeletal muscle that receive acetylcholine released to signal for muscular contraction. In the immune system, nAChRs regulate inflammatory processes and signal through distinct intracellular pathways. In insects, the cholinergic system is limited to the central nervous system.
  The nicotinic receptors are considered cholinergic receptors, since they respond to acetylcholine.
context_section_description: Nicotinic receptors, with a molecular mass of 290 kDa, are made up of five subunits, arranged symmetrically around a central pore. Each subunit comprises four transmembrane domains with both the N- and C-terminus located extracellularly. They possess similarities with GABAA receptors, glycine receptors, and the type 3 serotonin receptors (which are all ionotropic receptors), or the signature Cys-loop proteins.
  In vertebrates, nicotinic receptors are broadly classified into two subtypes based on their primary sites of expression: muscle-type nicotinic receptors and neuronal-type nicotinic receptors.  In the muscle-type receptors, found at the neuromuscular junction, receptors are either the embryonic form, composed of α1, β1, γ, and δ subunits in a 2:1:1:1 ratio, or the adult form composed of α1, β1, δ, and ε subunits in a 2:1:1:1 ratio.  The neuronal subtypes are various homomeric (all one type of subunit) or heteromeric (at least one α and one β) combinations of twelve different nicotinic receptor subunits: α2−α10 and β2−β4.  Examples of the neuronal subtypes include: (α4)₃(β2)₂, (α4)₂(β2)₃, (α3)₂(β4)₃, α4α6β3(β2)₂, (α7)₅, and many others.  In both muscle-type and neuronal-type receptors, the subunits are very similar to one another, especially in the hydrophobic regions.
  A number of electron microscopy and x-ray crystallography studies have provided very high resolution structural information for muscle and neuronal nAChRs and their binding domains.
caption: Nicotinic receptor structure
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