title: A photochromic histidine kinase rhodopsin (HKR1) that is bimodally switched by ultraviolet and blue light.
abstract: Rhodopsins are light-activated chromoproteins that mediate signaling processes via transducer proteins or promote active or passive ion transport as ion pumps or directly light-activated channels. Here, we provide spectroscopic characterization of a rhodopsin from the Chlamydomonas eyespot. It belongs to a recently discovered but so far uncharacterized family of histidine kinase rhodopsins (HKRs). These are modular proteins consisting of rhodopsin, a histidine kinase, a response regulator, and in some cases an effector domain such as an adenylyl or guanylyl cyclase, all encoded in a single protein as a two-component system. The recombinant rhodopsin fragment, Rh, of HKR1 is a UVA receptor (λ(max) = 380 nm) that is photoconverted by UV light into a stable blue light-absorbing meta state Rh-Bl (λ(max) = 490 nm). Rh-Bl is converted back to Rh-UV by blue light. Raman spectroscopy revealed that the Rh-UV chromophore is in an unusual 13-cis,15-anti configuration, which explains why the chromophore is deprotonated. The excited state lifetime of Rh-UV is exceptionally stable, probably caused by a relatively unpolar retinal binding pocket, converting into the photoproduct within about 100 ps, whereas the blue form reacts 100 times faster. We propose that the photochromic HKR1 plays a role in the adaptation of behavioral responses in the presence of UVA light.
authors.affiliation: Institute of Biology, Experimental Biophysics, Humboldt-Universität zu Berlin, 10115 Berlin, Germany.
authors.forename: Meike
authors.initials: M
authors.lastname: Luck
authors.forename: Tilo
authors.initials: T
authors.lastname: Mathes
authors.forename: Sara
authors.initials: S
authors.lastname: Bruun
authors.forename: Roman
authors.initials: R
authors.lastname: Fudim
authors.forename: Rolf
authors.initials: R
authors.lastname: Hagedorn
authors.forename: Tra My
authors.initials: TM
authors.lastname: Tran Nguyen
authors.forename: Suneel
authors.initials: S
authors.lastname: Kateriya
authors.forename: John T M
authors.initials: JT
authors.lastname: Kennis
authors.forename: Peter
authors.initials: P
authors.lastname: Hildebrandt
authors.forename: Peter
authors.initials: P
authors.lastname: Hegemann
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology* / Q000528:radiation effects; D000262:Adenylyl Cyclases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D016825:Chlamydomonas reinhardtii / Q000201:enzymology* / Q000235:genetics; D006162:Guanylate Cyclase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000071677:Histidine Kinase; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D012243:Rhodopsin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D010940:Plant Proteins; D012243:Rhodopsin; D011494:Protein Kinases; D000071677:Histidine Kinase; D000262:Adenylyl Cyclases; D006162:Guanylate Cyclase