Engineerng a "nano-leaf" based on hydrogenase and PSII for hydrogen production from solar energy

The immobilisation of natural hydrogenases and photosystem II (PSII) onto electrodes with efficient electronic coupling so as generate hydrogen using electrons and protons derived from light- driven water splitting,represent an electrochemical converter of solar energy into valuable fuel. In such a system the hydrogenase would represent the cathodic side working in combination with a separate anodic electrode binding PSII. The expression in E. coli of the [FeFe] hydrogenase HydA1 from the green alga Chlamydomonas reinhardtii has recently been achieved by co-expressing accessory proteins involved in assembling the active site. This heterologous expression gives us the opportunity of genetically engineering the enzyme to achieve better stability/activity and with lower oxygen sensitivity as well as enhancing and orienting protein/electrode interaction for optimising the performance of the device. The expression and affinity purification of the recombinant hydrogenase provided protein which was checked for its spectroscopic properties (by circular dicroism),protein stability (pH, temperature and oxygen sensitivity) and the hydrogen production activity. The immobilisation and electrochemistry of hydrogenase is being investigated using graphite and TiO2 electrodes. For the anodic surface, PSII from Thermosynechococcus elongatus was isolated from a modified CP43-(His6)strain for oriented immobilisation. The protein was bound on glassy carbon electrode modified with DDAB (didecyldimethylammonium bromide) and a photo- catalytic current was recorded which is inhibited by the addition of DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea), a compound which specifically impairs electron flow from the PSII QB site.