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Details of Grant 

EPSRC Reference: EP/K000764/1
Title: International Collaboration in Chemistry: BLUF Domain blue light photosensors - a paradigm for optogenetics
Principal Investigator: Meech, Professor S
Other Investigators:
Researcher Co-Investigators:
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Department: Chemistry
Organisation: University of East Anglia
Scheme: Standard Research
Starts: 18 March 2013 Ends: 17 March 2016 Value (£): 283,817
EPSRC Research Topic Classifications:
Chemical Structure Physical Organic Chemistry
Protein chemistry
EPSRC Industrial Sector Classifications:
No relevance to Underpinning Sectors
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Summary on Grant Application Form
A wide variety of organisms sense and respond to light. The most obvious examples are photosynthesis in plants, which converts sunlight into chemical energy, and the response of the vision pigments, which translate the photons falling onto the retina into vision signals in the brain. The protein complexes responsible for these processes - photosystem I and rhodopsin respectively - have been studied for many years. Although our understanding of them is still evolving great progress has been made in determining the mechanism of the photoresponse. In recent years a new family of light sensitive proteins, the photoactive flavoproteins, have been found widely in plants and bacterial. These are as yet much less well characterised but have been shown to be the meditating factor in a variety of photosensitive responses. For example the photophobic response which causes bacteria to swim away from a damaging light source, phototaxis in plants, the orientation of leaves to preferentially absorb the sun and photogenetic control, by which bacteria turn off unnecessary biosynthesis in strong light. An example of the latter process is the protein AppA, which in the dark binds a repressor protein PpsR, but in light undergoes a structure change to release the repressor. This is the protein complex we will study.

In the work proposed here we will combine two types of advanced technology. First advanced spectroscopic methods will be used to probe structural dynamics of flavoproteins in response to light absorption. In particular we will combine spectroscopy in the visible region of the spectrum, to tell us about the processes in the flavoprotein occurring after blue light absorption, with infra-red measurements which yield structural dynamics. Because of the fast nature of the primary processes and the low concentration of the protein extremely sensitive methods, such as those developed in our laboratories and in the Laser for Science Facility at the Harwell Research Complex, are required. For the structural studies in the IR it will also be necessary to exploit the new femto- to millisecond methods under development at the LSF Harwell. These will allow us to study for the first time the complete structural dynamics responsible for the biological event.

The second critical tool is advanced methods of chemical biology. It is now possible to site specifically label a protein with unnatural amino acids. We plan to exploit this recent development in two ways. First we will place residues containing specific IR labels, which absorb at characteristic frequencies at known sites along the pathway thought to be involved in the structure change. By timing the delay between flavin excitation and the onset of change in the specific residue we will be able to map out the detailed mechanism of the structure change. Next we will modify the residues in the vicinity of the flavin to alter the primary events which trigger structural change. In this way we aim to optimize and control the flavin photoresponse.

It is this last aspect, the potential to control the photoresponse, which provides an exciting opportunity to apply this new knowledge in a much wider context. Since 2009 the idea of optically controlling intracellular responses - optogenetics - has been generating great excitement. This idea has its origins in the success of GFP technology, where a fluorescent protein (GFP) was encoded to label a specific protein in a living cell. In opto-genetics a protein with a specific optically addressable function is genetically encoded in a similar way. Once in place the function can be stimulated by light. AppA is an excellent candidate, particularly if the light induced complex dissociation mechanism of AppA can be recruited and controlled to bind and release an arbitrary partner (for example a drug molecule). Such an optically addressable function would be an immense step forward.

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