Origin and molecular evolution of ionotropic glutamate receptors.

This article provides a review of approaches to identification of the pathways of the molecular evolution of glutamate receptors. Extensive evidence has now accumulated on the homology of glutamate-binding proteins with the ability to function as ligand-activated channels. However, knowledge of the amino acid sequences of the polypeptides forming these channels is a necessary but insufficient condition for identifying their origin and changes during evolution. Natural selection of protein molecules appears to have identified and fixed their functional nature. Molecular and functional approaches should therefore complement each other in studies of protein evolution. Studies of glutamate receptor channels in vertebrates and invertebrates provide an example showing how knowledge of the spatial organization and the details of the mechanisms of operation allows relationships to be identified and possible pathways of the molecular evolution of receptors to be established.