title: Time-resolved tracking of interprotein signal transduction: Synechocystis PixD-PixE complex as a sensor of light intensity.
abstract: PixD (Slr1694) is a blue light receptor that contains a BLUF (blue light sensors using a flavin chromophore) domain. A protein-protein interaction between PixD and a response regulator PixE (Slr1693) is essential to achieve light signal transduction for phototaxis of the species. Although the initial photochemical reaction of PixD, the red shift of the flavin absorption spectrum, has been investigated, the subsequent reaction dynamics remain largely unresolved. Only the disassembly of the PixD(10)-PixE(5) dark complex has been characterized by static size exclusion chromatography. In this report, interprotein reaction dynamics were examined using time-resolved transient grating spectroscopy. The dissociation process was clearly observed as the light-induced diffusion coefficient change in the time domain, and the kinetics was determined. More strikingly, disassembly was found to take place only after photoactivation of two PixD subunits in the complex. This result suggests that the biological response of PixD does not follow a linear correlation with the light intensity but appears to be light-intensity-dependent.
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Tanaka
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Nakasone
authors.forename: Koji
authors.initials: K
authors.lastname: Okajima
authors.forename: Masahiko
authors.initials: M
authors.lastname: Ikeuchi
authors.forename: Satoru
authors.initials: S
authors.lastname: Tokutomi
authors.forename: Masahide
authors.initials: M
authors.lastname: Terazima
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008027:Light; D055537:Light Signal Transduction; D008958:Models, Molecular; D020283:Photoreceptors, Microbial / Q000737:chemistry / Q000378:metabolism*; D060066:Protein Interaction Maps; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D013057:Spectrum Analysis; D046939:Synechocystis / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; D021122:Protein Subunits