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My research focuses on a light-signaling molecule, a protein called AppA. It comes from a photosynthetic bacterium Rhodobacter sphaeroides and functions as an anti-repressor and antagonist to PpsR, which has affinity to the promoter of the photosynthetic gene cluster. I am trying to understand the molecular basis of the light signal transfer between these two proteins. So, far, we have solved the structure of one of the domains of AppA, called BLUF domain (Blue-Light Using FAD), carrying out the light sensing function through the light absorption of its FAD molecule and conformational change. Recently we investigated the fast events of FAD light absorption that lead to a formation of a reversible light state using time-resolved pump-probe absorption spectroscopy. The second domain of AppA binds heme molecule and likely participates in redox signaling, as AppA is proposed to be an oxygen sensor as well as light sensor. Both signals then contribute to the control of the photosynthesis gene transcription.
I also attempt to crystallize several other proteins. At this point it’s a membrane protein, RegB, a histidine kinase from Rhodobacter capsulatus.
Recent publications:
 Kraft, B. J., Masuda, S., Kikuchi, J., Dragnea, V., Tollin, G., Zaleski, J. M., and Bauer, C. E. (2003) Spectroscopic and mutational analysis of the blue-light photoreceptor AppA: a novel photocycle involving flavin stacking with an aromatic amino acid, Biochemistry 42, 6726-34.
Anderson, S., Dragnea, V., Masuda, S., Ybe, J., Moffat, K., and Bauer, C. (2005) Structure of a novel photoreceptor, the BLUF domain of AppA from Rhodobacter sphaeroides, Biochemistry 44, 7998-8005.
Dragnea, V., Waegele, M., Balascuta, S., Bauer, C., and Dragnea, B. (2005) Time-resolved spectroscopic studies of the AppA blue-light receptor BLUF domain from Rhodobacter sphaeroides, Biochemistry 44, 15978-85.
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Vladimira Dragnea, Ph.D.
