title: Molecular properties of rhodopsin and rod function.
abstract: Signal transduction in rod cells begins with photon absorption by rhodopsin and leads to the generation of an electrical response. The response profile is determined by the molecular properties of the phototransduction components. To examine how the molecular properties of rhodopsin correlate with the rod-response profile, we have generated a knock-in mouse with rhodopsin replaced by its E122Q mutant, which exhibits properties different from those of wild-type (WT) rhodopsin. Knock-in mouse rods with E122Q rhodopsin exhibited a photosensitivity about 70% of WT. Correspondingly, their single-photon response had an amplitude about 80% of WT, and a rate of decline from peak about 1.3 times of WT. The overall 30% lower photosensitivity of mutant rods can be explained by a lower pigment photosensitivity (0.9) and the smaller single-photon response (0.8). The slower decline of the response, however, did not correlate with the 10-fold shorter lifetime of the meta-II state of E122Q rhodopsin. This shorter lifetime became evident in the recovery phase of rod cells only when arrestin was absent. Simulation analysis of the photoresponse profile indicated that the slower decline and the smaller amplitude of the single-photon response can both be explained by the shift in the meta-I/meta-II equilibrium of E122Q rhodopsin toward meta-I. The difference in meta-III lifetime between WT and E122Q mutant became obvious in the recovery phase of the dark current after moderate photobleaching of rod cells. Thus, the present study clearly reveals how the molecular properties of rhodopsin affect the amplitude, shape, and kinetics of the rod response.
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University and Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Kyoto 606-8502, Japan.
authors.forename: Hiroo
authors.initials: H
authors.lastname: Imai
authors.forename: Vladimir
authors.initials: V
authors.lastname: Kefalov
authors.forename: Keisuke
authors.initials: K
authors.lastname: Sakurai
authors.forename: Osamu
authors.initials: O
authors.lastname: Chisaka
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Ueda
authors.forename: Akishi
authors.initials: A
authors.lastname: Onishi
authors.forename: Takefumi
authors.initials: T
authors.lastname: Morizumi
authors.forename: Yingbin
authors.initials: Y
authors.lastname: Fu
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Ichikawa
authors.forename: Kei
authors.initials: K
authors.lastname: Nakatani
authors.forename: Yoshihito
authors.initials: Y
authors.lastname: Honda
authors.forename: Jeannie
authors.initials: J
authors.lastname: Chen
authors.forename: King-Wai
authors.initials: KW
authors.lastname: Yau
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Shichida
mesh_terms: D000818:Animals; D019393:Arrestin; D006207:Half-Life; D007700:Kinetics; D051379:Mice; D020125:Mutation, Missense; D017785:Photons; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology*; D012243:Rhodopsin / Q000235:genetics; D014785:Vision, Ocular
chemical_list: D019393:Arrestin; D012243:Rhodopsin