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The major role of G-protein-coupled receptors is to transmit signals into the cell (Chapter 6 Section D). They are characterized by seven transmembrane segments. This class of membrane proteins can respond to a wide range of agonists, including photon, amines, hormones, neurotransmitters and proteins. Some agonists bind to the extracellular loops of the receptor, others may penetrate into the transmembrane region. (a)
Figure 2-F-1. (a) Schematic drawing of the transmembrane topology of the G-protein-coupled receptor, which is characterized by seven transmembrane segments. None of the structures of G-protein-coupled receptors has been determined yet, but their transmembrane structures are expected to be similar to bacteriorhodopsin (a proton pump) as shown in (b) (side view) and (c) (top view). PDB ID = 1AT9.
Illustrations: Schematic presentation of the general structure of GPCRs and receptor-ligand interactions - J. Biol. Chem., 1998. Database: GPCRDB: G-Protein-Coupled Receptor Database
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