AppA, a Redox Regulator of Photosystem Formation inRhodobacter sphaeroides 2.4.1, Is a Flavoprotein

作者：Mark Gomelsky, Samuel Kaplan · 发表于：Journal of Biological Chemistry · 年份：1998 · DOI：10.1074/jbc.273.52.35319 · 被引用次数：120 · 研究领域：Photosynthetic Processes and Mechanisms、Microbial Community Ecology and Physiology、Microbial bioremediation and biosurfactants

The AppA protein is required for increased photosystem gene expression upon transition of the facultatively photoheterotrophic bacterium Rhodobacter sphaeroides 2.4.1 from aerobic to anaerobic photosynthetic conditions. AppA shows no obvious similarity to proteins with established function. Genetic evidence suggests that its effect is exerted through modulation of the activity of the repressor PpsR, which controls expression of multiple photosystem genes. To gain insight into the nature of AppA involvement in redox-dependent photosystem gene expression, the appA gene was overexpressed in Escherichia coli. AppA was produced as insoluble inclusion bodies. The purified inclusion bodies were found to contain FAD. By overexpressing various deletion derivatives, we were able to localize the region of AppA sufficient for FAD binding to approximately 120 amino-terminal residues. To assess the role of FAD binding in AppA function, we constructed an AppA derivative lacking the entire FAD binding domain. Surprisingly, this derivative complemented the AppA null mutant undergoing transition from aerobic to anaerobic photosynthetic growth conditions almost to the same extent as the full-length AppA protein. When the sequence of the amino-terminal portion of AppA was examined, it was shown not to contain any known flavin binding motifs. However, two open reading frames of unknown function, showing significant similarity to the amino terminus of AppA, were identified, i.e. Synechocystis sp. ...