title: PixE promotes dark oligomerization of the BLUF photoreceptor PixD.
abstract: Cyanobacteria perceive and move (phototax) in response to blue light. In this study, we demonstrate that the PixD blue light-sensing using FAD (BLUF) photoreceptor that governs this response undergoes changes in oligomerization state upon illumination. Under dark conditions we observed that PixD forms a large molecular weight complex with another protein called PixE. Stoicheometric analyses, coupled with sedimentation equilibrium and size exclusion chromatography, demonstrates that PixE drives aggregation of PixD dimers into a stable PixD(10)-PixE(5) complex under dark conditions. Illumination of a flavin chromophore in PixD destabilizes the PixD(10)-PixE(5) complex into monomers of PixE and dimers of PixD. A crystallographic structure of PixD, coupled with Gibbs free energy calculation between interacting faces of PixD, lends to a model in which a light induces a conformational change in a critical PixD-interfacing loop that results in destabilization of the PixD(10)-PixE(5) complex.
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN 47405, USA.
authors.forename: Hua
authors.initials: H
authors.lastname: Yuan
authors.forename: Carl E
authors.initials: CE
authors.lastname: Bauer
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002151:Calorimetry; D002850:Chromatography, Gel; D003116:Color; D000458:Cyanobacteria / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D007700:Kinetics; D010786:Photoreceptor Cells / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D013053:Spectrophotometry
chemical_list: D018528:ATP-Binding Cassette Transporters