PixE promotes dark oligomerization of the BLUF photoreceptor PixD
Yuan, Hua | Bauer, Carl E.
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 PixD₁₀--PixE₅ complex under dark conditions. Illumination of a flavin chromophore in PixD destabilizes the PixD₁₀-PixE₅ 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 PixD₁₀-PixE₅ complex.Show more [+] Less [-]