BibSonomy publications for /concept/tag/Escherichia_coli+DNA-Binding_ProteinsWed May 07 15:52:44 CEST 2008Journal of bacteriologyMarchPMID: 172090352274-82The AppA and PpsR proteins from Rhodobacter sphaeroides can establish a redox-dependent signal chain but fail to transmit blue-light signals in other bacteria1892007Light Microbial Oxidation-Reduction Signal_Transduction Bacterial_Proteins Repressor_Proteins Bacterial Rhodobacter_sphaeroides Escherichia_coli IFZ Gene_Expression_Regulation Photoreceptors Flavoproteins DNA-Binding_Proteins Photosynthesis Trans-Activators Oxygen Rhodobacter_capsulatus Paracoccus_denitrificans The AppA protein of Rhodobacter sphaeroides has the unique ability to sense and transmit redox and light signals. In response to decreasing oxygen tension, AppA antagonizes the transcriptional regulator PpsR, which represses the expression of photosynthesis genes, including the puc operon. This mechanism, which is based on direct protein-protein interaction, is prevented by blue-light absorption of the BLUF domain located in the N-terminal part of AppA. In order to test whether AppA and PpsR are sufficient to transmit redox and light signals, we expressed these proteins in three different bacterial species and monitored oxygen- and blue-light-dependent puc expression either directly or by using a luciferase-based reporter construct. The AppA/PpsR system could mediate redox-dependent gene expression in the alphaproteobacteria Rhodobacter capsulatus and Paracoccus denitrificans but not in the gammaproteobacterium Escherichia coli. Analysis of a prrA mutant strain of R. sphaeroides strongly suggests that light-dependent gene expression requires a balanced interplay of the AppA/PpsR system with the PrrA response regulator. Therefore, the AppA/PpsR system was unable to establish light signaling in other bacteria. Based on our data, we present a model for the interdependence of AppA/PpsR signaling and the PrrA transcriptional activator.Wed May 07 15:52:44 CEST 2008Molecular microbiologyMayPMID: 175019301090-104A haem cofactor is required for redox and light signalling by the AppA protein of Rhodobacter sphaeroides642007Molecular_Sequence_Data IFZ Heme Rhodobacter_sphaeroides Sequence_Alignment Electrophoretic_Mobility_Shift_Assay Tertiary Signal_Transduction Recombinant_Proteins Oxidation-Reduction Coenzymes Biological DNA-Binding_Proteins Spectrum_Analysis Hemin Gene_Expression_Regulation Flavoproteins Bacterial Repressor_Proteins Models Bacterial_Proteins Sequence_Deletion Light Protein_Binding Amino_Acid_Sequence Escherichia_coli Protein_Structure The AppA protein of Rhodobacter sphaeroides is unique in its ability to sense and transmit redox signals as well as light signals. By functioning as antagonist to the PpsR transcriptional repressor, it regulates the expression of photosynthesis genes in response to these environmental stimuli. Here we show binding of the cofactor haem to a domain in the C-terminal part of AppA and redox activity of bound haem. This is supported by the findings that: (i) the C-terminal domain of AppA (AppADeltaN) binds to haemin agarose, (ii) AppADeltaN isolated from Escherichia coli shows absorbance at 411 nm and absorbances at 424 nm and 556 nm after reduction with dithionite and (iii) AppADeltaN can be reconstituted with haem in vitro. Expression of AppA variants in R. sphaeroides reveals that the haem binding domain is important for normal expression levels of photosynthesis genes and for normal light regulation in the presence of oxygen. The haem cofactor affects the interaction of the C-terminal part of AppA to PpsR but also its interaction to the N-terminal light sensing AppA-BLUF domain. Based on this we present a model for the transmission of light and redox signals by AppA.