A pentameric protein is a quaternary protein structure that consists of five protein subunits. These sub-units come together to form a channel. Each channel consist of two alpha chain, one beta, one gamma and one delta chains. These five chains assemble together (along with certain receptors like protons or acetylcholine) forming the structure of the channel. A Ligand-gated ion channel on the post-synaptic junction of the muscle-end plate is an example of such a channel. They are acetylcholine-operated ion channels, which means that acetylcholine brings about a conformational change. The channel allows the free movement of the cations like Na and K when acetyl choline binds to its receptors.