5-HT Receptor MX Helix Contributes to Receptor Function.

5-HT receptors are members of the family of pentameric ligand-gated ion channels. Each subunit has an extracellular, transmembrane, and intracellular domain. Only part of the intracellular domain structure has been solved, revealing it contains two α-helical segments; one, the MA helix, is an extension of M4, while the other, the MX helix, is formed from residues located close to the end of M3.