title: Intramolecular interactions that induce helical rearrangement upon rhodopsin activation: light-induced structural changes in metarhodopsin IIa probed by cysteine S-H stretching vibrations.
abstract: Rhodopsin undergoes rearrangements of its transmembrane helices after photon absorption to transfer a light signal to the G-protein transducin. To investigate the mechanism by which rhodopsin adopts the transducin-activating conformation, the local environmental changes in the transmembrane region were probed using the cysteine S-H group, whose stretching frequency is well isolated from the other protein vibrational modes. The S-H stretching modes of cysteine residues introduced into Helix III, which contains several key residues for the helical movements, and of native cysteine residues were measured by Fourier transform infrared spectroscopy. This method was applied to metarhodopsin IIa, a precursor of the transducin-activating state in which the intramolecular interactions are likely to produce a state ready for helical movements. No environmental change was observed near the ionic lock between Arg-135 in Helix III and Glu-247 in Helix VI that maintains the inactive conformation. Rather, the cysteine residues that showed environmental changes were located around the chromophore, Ala-164, His-211, and Phe-261. These findings imply that the hydrogen bond between Helix III and Helix V involving Glu-122 and His-211 and the hydrophobic packing between Helix III and Helix VI involving Gly-121, Leu-125, Phe-261, and Trp-265 are altered before the helical rearrangement leading toward the active conformation.
authors.affiliation: From the Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan, the Graduate School of Materials Science, Nara Institute of Science and Technology, Nara, 630-0192, Japan.
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Yamazaki
authors.affiliation: From the Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Nagata
authors.affiliation: From the Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan, the Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka 558-8585, Japan, and.
authors.forename: Akihisa
authors.initials: A
authors.lastname: Terakita
authors.affiliation: From the Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan, the Department of Frontier Materials, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Kandori
authors.affiliation: From the Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Shichida
authors.affiliation: From the Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan, imamoto@rh.biophys.kyoto-u.ac.jp.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Imamoto
mesh_terms: D000595:Amino Acid Sequence; D003545:Cysteine / Q000737:chemistry*; D057809:HEK293 Cells; D006801:Humans; D008027:Light; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010713:Phosphatidylcholines / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary / Q000528:radiation effects; D012243:Rhodopsin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014732:Vibration
chemical_list: D008081:Liposomes; D010713:Phosphatidylcholines; C013110:metarhodopsins; D012243:Rhodopsin; D003545:Cysteine
keywords: Fourier Transform IR (FTIR); G-protein-coupled Receptor (GPCR); Phototransduction; Protein Conformation; Rhodopsin; Vision