Structural characterization and binding sites of G-protein-coupled receptors

G-protein-coupled proteins constitute a superfamily of integral membrane proteins encompassing hundreds of receptors for all types of chemical messengers, as well as, for example, the key molecules of our light and smell sensory systems, bioactive amines, peptide hormones, neurotransmitters and even proteins. Because of their complicated organization with the characteristic seven transmembrane segments (7TM) it has as yet been impossible to structurally characterize these proteins by crystallography or magnetic resonance. However, a number of indirect methods to study the structure, ligand binding and signal transduction capacity of these proteins are known and summarized in this review.