Subunits: Building blocks of nicotinic acetylcholine receptors (nAChR)

Subunits are the building blocks of nicotinic acetylcholine receptors (nAChR), which are neurotransmitter-gated ion channels. Opening of the channel is triggered by nicotine or acetylcholine and allows positively charged ions to flow down their concentration gradients across the plasma membrane.
 
Nicotinic acetylcholine receptors exist as diverse subtypes expressed in different tissues or cells.  For example, nicotinic receptors in adult mammalian muscle are different from two kinds of receptors in autonomic neurons and from predominant kinds of receptors in the brain. Each distinct nicotinic receptor subtypes is composed of different combinations of genetically distinct subunits. Each subunit is a transmembrane protein. It is thought that five subunits combine to form a complete nicotinic receptor. Subunits assemble similar to staves of a barrel to create a void that is the ion channel.

Evolutionary and protein sequence relationships between nicotinic receptor subunits from different species are known (see Lukas, 1998, and Lukas et al., 1999, for details). Most closely related subunits include alpha 4 and alpha 2, alpha 6 and alpha 3, and beta 2 and beta 3. The most ancient subunits (e.g., alpha 7) also form the simplest types of receptors containing only those subunits.

Genetic variations in nicotinic receptor subunits exist across individuals. In some cases, these variations contribute to or cause neurological diseases. They could also influence behavior, such as susceptibility to use of tobacco products. 

> For more information about nicotine receptors, visit The Ligand Gated Ion Channel Database. [This website link is provided for your convenience only. Barrow Neurological Institute neither endorses nor is responsible for the content in any way.]

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Barrow Neurological Institute of St. Joseph's Hospital and Medical Center, Phoenix, Arizona