title: Comparative investigation of the LOV1 and LOV2 domains in Adiantum phytochrome3.
abstract: Phototropin (phot) is a blue-light photoreceptor for phototropic responses, relocation of chloroplasts, and stomata opening in plants. Phototropin has two chromophore-binding domains named LOV1 and LOV2 in its N-terminal half, each of which binds a flavin mononucleotide (FMN) noncovalently. The C-terminal half is a Ser/Thr kinase. A transgenic study of Arabidopsis suggested that only LOV2 domain is necessary for the kinase activity, whereas X-ray crystallographic structures of LOV1 and LOV2 domains are almost identical. These facts imply that the detailed structures and/or structural changes are different between LOV1 and LOV2 domains. In this study, we compared light-induced structural changes of the LOV1 and LOV2 domains of a phototropin, Adiantum phytochrome3 (phy3), by means of UV-visible and Fourier transform infrared (FTIR) spectroscopy. Photochemical properties of an adduct formation between FMN and a cysteine are essentially similar between phy3-LOV1 and phy3-LOV2. On the other hand, the S-H group of the reactive cysteine forms a hydrogen bond in phy3-LOV1, which is strengthened at low temperatures. This is possibly correlated with the fact that no adduct formation takes place for phy3-LOV1 at 77 K as revealed by the UV-visible absorption spectra. The most prominent difference was seen in the amide-I vibration that monitors the secondary structure of peptide backbone. Protein structural changes in phy3-LOV2 involve the regions of loops, alpha-helices, and beta-sheets, which differ significantly among various temperatures. Extended protein structural changes are probably correlated with the signal transduction activity of LOV2. In contrast, protein structural changes were very small in phy3-LOV1, and they were almost temperature independent. The photocycle of phy3-LOV1 takes 3.1 h, being more than 100 times longer than that of phy3-LOV2. These facts suggest that Adiantum phy3-LOV1 does not work for light sensing, being consistent with the previous transgenic study of Arabidopsis. It is likely that plants utilize a unique protein architecture (LOV domain) for different functions by regulating their protein structural changes.
authors.affiliation: Department of Materials Science and Engineering, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Iwata
authors.forename: Dai
authors.initials: D
authors.lastname: Nozaki
authors.forename: Satoru
authors.initials: S
authors.lastname: Tokutomi
authors.forename: Hideki
authors.initials: H
authors.lastname: Kandori
mesh_terms: D035681:Adiantum; D056931:Cryptochromes; D005420:Flavoproteins / Q000737:chemistry*; D005615:Freezing; D008027:Light; D010100:Oxygen / Q000737:chemistry; D010446:Peptide Fragments / Q000737:chemistry; D010834:Phytochrome / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D056931:Cryptochromes; D005420:Flavoproteins; D010446:Peptide Fragments; D010834:Phytochrome; D010100:Oxygen