Photoactivation: the assembly of the active site of the water oxidising enzyme

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This project is aimed at understanding how Photosystem 2 (PS2) works. This enzyme is found in plants, algae and some microbes. It is the main solar converter of photosynthesis, the process by which solar energy is converted to the chemical fuels used for powering life . Nearly all life on the planet runs on energy that came from photosynthesis. PS2 is important not just as a solar collector; it is the only enzyme that has is able to use water to make fuel. Water (H2O) is very stable; it takes a lot of energy to rip it apart, two molecules at a time, to provide electrons for fuel making. PS2 is able to do this using solar energy. This reaction releases protons (4H+) and oxygen gas (O2) as side-products.PS2 evolved in bacteria on the primitive Earth when O2 was absent. This was a key event in the evolution of life. The O2 released could be used for respiration, a much more efficient way of using biological fuels than existed previously. This drastic jump in the efficiency of energy use meant that biology could become much more complicated: multicellular life could develop. The O2 escaped to the atmosphere and was converted to ozone by UV radiation. The ozone formed then blocked further deadly UV from reaching the surface of the planet. Overall, PS2 provided the energy for life to flourish, allowed life to come out from under the stones and to develop into life as we know it. It is the enzyme that changed the planet.This project is focused on how PS2 works and how the part that reacts with water is built into the part that does the solar conversion. This building-in process is called "photoactivation" and it occurs when the enzyme is first made and when it is repaired. Given that every plant and nearly every photosynthetic microbe has many millions of these enzymes and that each PS2 needs to be repaired about every 30 minutes, then there is rather a lot of photoactivation going on. And yet very little is known about it. It is known that during photoactivation PS2 is particularly sensitive to being damaged by light. Under stress conditions (too hot, too cold, too dry, etc), this can end up killing the cell and this can limit the yields of crops and determine whether the organism lives or dies. We wish to understand what is going on here. The work is likely to be useful to farmers, the agri-science industry, ecologists etc because it should allow methods and processes to be developed for improving yields of crops and improving survival of photosynthetic species in a changing environment. The fossil fuels represent the product of eons of photosynthesis converting solar energy to biomass by the capture CO2 from the ancient atmosphere. Humans are in the process of returning the CO2 to the atmosphere in what is "the blink of an eye" on a planetary time-scale and this is changing the planet. Perhaps the biggest challenge to scientists at present is to solve the energy/climate crisis by finding alternatives to fossil fuels. It is becoming clear that solar energy is the only alternative energy source that is big enough to do this. While converting solar energy to electricity is straightforward, to solve our energy needs, particularly for transport, we require fuels. Solar fuel production is a crucial requirement. Natural photosynthesis is the biggest solar fuel producer however it does this slowly and inefficiently and we cannot rely on natural photosynthesis to replace fossil fuels that took eons to accumulate. Artificial solar fuel production aims to "cherry-pick" the best features from natural photosynthesis to make a more efficient artificial version. The water splitting enzyme, the enzyme that changed the planet, is the main focus of scrutiny for these studies. The current research will provide key information on how this enzyme works, how it is made and how it is repaired: information that is key for solar fuel production by artificial photosynthesis.