title: Origin of the low thermal isomerization rate of rhodopsin chromophore.
abstract: Low dark noise is a prerequisite for rod cells, which mediate our dim-light vision. The low dark noise is achieved by the extremely stable character of the rod visual pigment, rhodopsin, which evolved from less stable cone visual pigments. We have developed a biochemical method to quickly evaluate the thermal activation rate of visual pigments. Using an isomerization locked chromophore, we confirmed that thermal isomerization of the chromophore is the sole cause of thermal activation. Interestingly, we revealed an unexpected correlation between the thermal stability of the dark state and that of the active intermediate MetaII. Furthermore, we assessed key residues in rhodopsin and cone visual pigments by mutation analysis and identified two critical residues (E122 and I189) in the retinal binding pocket which account for the extremely low thermal activation rate of rhodopsin.
authors.affiliation: Cellular Informatics Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan.
authors.forename: Masataka
authors.initials: M
authors.lastname: Yanagawa
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Kojima
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Yamashita
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Imamoto
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Take
authors.initials: T
authors.lastname: Matsuyama
authors.affiliation: Department of Chemistry, Columbia University, New York, NY 10027, USA.
authors.forename: Koji
authors.initials: K
authors.lastname: Nakanishi
authors.affiliation: Department of Organic Chemistry for Life Science, Kobe Pharmaceutical University, Kobe 658-8558, Japan.
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Yamano
authors.affiliation: Department of Organic Chemistry for Life Science, Kobe Pharmaceutical University, Kobe 658-8558, Japan.
authors.forename: Akimori
authors.initials: A
authors.lastname: Wada
authors.affiliation: Cellular Informatics Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Sako
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Shichida
mesh_terms: D000596:Amino Acids; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization; D012160:Retina / Q000378:metabolism; D012243:Rhodopsin / Q000737:chemistry* / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D000596:Amino Acids; D012243:Rhodopsin