Sequence analyses of G-protein-coupled receptors: similarities to rhodopsin

G-protein-coupled receptors (GPCRs) constitute a large superfamily of receptor proteins responsible for signal transduction (see http://www.gpcr.org/7tm). Throughout all higher organisms, these receptors mediate recognition of environmental stimuli like light, odor, and taste, but also hormonal and other types of communications across plasma membranes (). They are also important targets for pharmacological intervention via activating or blocking their action (). Three families of GPCRs were identified, with family A being by far the largest (reviewed in refs -). Its members are more closely related to each other within a few functional domains than those of the other families. In addition, numerous diseases have been linked to specific mutations within the genes encoding GPCRs, also making these receptors targets for specific therapeutic interventions including gene transfer (-).