Neurotransmitters are the chemical messenger released by neurons or nerve cells in order to carry the message signals across the gap between the nerve endings of a neuron and target cell. This is followed by a cascade of reactions or secondary effects resulting in either flow of ions across the cell membrane or switching on/off an enzyme (protein functioning) inside the target cell.
The interactions between the binding group of a messenger and binding region of receptor site on a protein are relatively weak because after carrying the message, the messenger leaves the receptor binding sites of protein. Thus, these interactions must be strong enough to carry the message, but must be weak enough for allowing the messenger to depart from the receptor site.
Neurotransmitters are the chemical messengers that vary greatly in their structure as well as complexity and interact with receptors of proteins. Glycine has simplest structure and is formally non-polar, but its side chain or R group does not make any real contribution to the hydrophobic interactions.
Glutamic acid, glycine, gamma-amino butyric acid and dopamine can take part in weak hydrogen interactions. Acetylcholine is involved in ionic interactions. Van der Waal interactions can also be observed during the interactions of binding groups with the binding sites of receptor.