Rhodopsin activation blocked by metal-ion-binding sites linking transmembrane helices C and F

• Published in: Nature (London) 1996-09, Vol.383 (6598), p.347-350
• Main Authors: Sheikh, Søren P, Zvyaga, Tatyana A, Lichtarge, Olivier, Sakmar, Thomas P, Bourne, Henry R
• Format: Article
• Language: English
• Subjects: Activation; Amino Acid Sequence; Amino acids; Animals; Binding Sites; Biological and medical sciences; Cattle; Cell Line; Cell Membrane - metabolism; Cell receptors; Cell structures and functions; Cytoplasm - metabolism; Fundamental and applied biological sciences. Psychology; Guanosine 5'-O-(3-Thiotriphosphate) - metabolism; Helices; Histidine - genetics; Histidine - metabolism; Humanities and Social Sciences; Ions; Joining; letter; Membranes; Metal ions; Miscellaneous; Molecular and cellular biology; Molecular biology; Molecular Sequence Data; multidisciplinary; Mutagenesis, Site-Directed; Photoreceptors; Protein Conformation; Protein Structure, Secondary; Proteins; Receptors; Receptors, Cell Surface - metabolism; Rhodopsin - antagonists & inhibitors; Rhodopsin - chemistry; Rhodopsin - genetics; Rhodopsin - metabolism; Science; Science (multidisciplinary); Spectrophotometry, Ultraviolet; Transducin - metabolism; Zinc - metabolism
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/383347a0

A LARGE superfamily of receptors containing seven transmembrane (TM) helices transmits hormonal and sensory signals across the plasma membrane to heterotrimeric G proteins at the cytoplasmic face of the membrane. To investigate how G-protein-coupled receptors work at the molecular level, we have engineered metal-ion-binding sites between TM helices to restrain activation-induced conformational change in specific locations. In rhodopsin, the photoreceptor of retinal rod cells, we substituted histidine residues for natural amino acids at the cytoplasmic ends of the TM helices C and F. The resulting mutant proteins were able to activate the visual G protein transducin in the absence but not in the presence of metal ions. These results indicate that the TM helices C and F are in close proximity and suggest that movements of these helices relative to one another are required for transducin activation. Thus a change in the orientations of TM helices C and F is likely to be a key element in the mechanism for coupling binding of ligands (or isomerization of retinal) to the activation of G-protein-coupled receptors.