EVOLUTIONARY HISTORY OF THE LIGAND-GATED ION-CHANNEL SUPERFAMILY OF RECEPTORS

The fast-acting ligand-gated ion channels (LGICs) constitute a group t hat encompasses nicotinic ACh, 5-HT3, GABA(A) and glycine receptors. U ndoubtedly, they all share a common evolutionary ancestor, and the gro up can therefore be considered to be a gene superfamily. Because the m embers of the superfamily are all receptors, it is reasonable to suppo se that their common ancestor must also have been some type of recepto r, and because the receptors are made of similar subunits, the ancesto r was probably homo-oligomeric. Although we failed to find a group of proteins that are related evolutionarily to this superfamily, the anal ysis of the evolutionary relationships within the superfamily is possi ble and can give rise to information about the evolution of the struct ure and function of present-day receptors and indeed of the nervous sy stem itself.