Molecule of the Month: Acetylcholine Receptor
The neurotransmitter acetylcholine opens a protein channel, stimulating muscle contraction
The Cascade of Contraction
Cobras and Curare
Exploring the Structure
Binding Site for Acetylcholine
Although there aren’t currently structures of acetylcholine receptor bound to acetylcholine, you can see how it binds by looking at a similar protein, acetylcholine-binding protein. This protein was discovered in certain sea slugs, where it modulates the signals carried by acetylcholine. The acetylcholine receptor (PDB entry 2bg9) is shown on the left, in the closed state before acetylcholine binds. The membrane-spanning region (shown in white) is composed of multiple alpha helices. Binding sites for acetylcholine (shown in lime green) can be found on two of the five chains, which are colored gray. A close-up of the acetylcholine binding site in its unbound state is shown at the top right. The similar portion of the acetylcholine binding protein (PDB entry 3wip) is shown on the bottom, with acetylcholine (colored pink) bound. Three aromatic amino acids (shown in lime green) form a cage around acetylcholine. Acetylcholine also forms close interactions with one backbone tryptophan as well as water molecule (light blue) which mediates bonds to a leucine and methionine (shown in green) on another chain. An unusual disulfide linkage (yellow) between two adjacent cysteines helps form the pocket for the acetylcholine molecule. Notice that these amino acids fold up around the neurotransmitter. As the binding site closes around acetylcholine, it shifts the conformation of the whole receptor, opening the pore through the membrane.
Click on the JSmol tab to explore these structures.
This JSMol was designed and illustrated by Xinyi Christine Zhang.
November 2005, David Goodsellhttp://doi.org/10.2210/rcsb_pdb/mom_2005_11