The nicotinic receptor—structure

The nicotinic receptor has been successfully isolated from the electric ray (Torpedo marmorata) found in the Atlantic Ocean and Mediterranean sea, allowing the receptor to be carefully studied. As a result, a great deal is known about its structure and operation. 

It is a protein complex made up of five subunits, two of which are the same. The five subunits (two alpha, one beta, gamma, and delta) form a cylindrical or barrel shape which traverses the cell membrane as shown in Fig. 11.42. 

A gating or lock system is controlled by the interaction of the receptor with acetylcholine. When acetylcholine is unbound the gate is shut. When acetylcholine binds the gate is opened. 

The amino acid sequence for each subunit has been established and it is known that there is extensive secondary structure. 

The binding site for acetylcholine is situated on the alpha subunit and therefore there are two binding sites per receptor protein. 

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