Structural biology: A moving story of receptors

Abstract

Animals sense light and chemical signals through proteins called G-protein-coupled receptors. The crystal structure of one such receptor in complex with a G-protein fragment shows how these receptors are activated.

Figure 1. Activation of a G-protein-coupled receptor

a, Rhodopsin, shown here in its inactivated conformation, is a light-sensing receptor found in cell membranes. It consists of a protein (opsin, green) and a ligand (retinal, yellow, also shown in its inactivated conformation). When activated by light, rhodopsin binds to part of an adjacent G protein (binding region in red), triggering a cascade of biological responses. The protein plug (blue) is part of the extracellular domain of opsin, and immobilizes the extracellular transmembrane segments of the receptor. b, Scheerer et al. have determined the activated structure of opsin in complex with the receptor-binding peptide fragment of the G protein (the Gα peptide). The most notable difference when compared with the inactivated receptor is that transmembrane helix 6 (TM-VI) has moved substantially outward (indicated by the red arrow), thereby creating the binding pocket for the G-protein peptide.