Integrating a photosynthetic protein into a bio-solar-photovoltaic for electricity production
Interest in renewable energy sources has grown due to the need to find a technology or fuel source to replace our dependence on fossil fuels, which emit large quantities of carbon dioxide into our atmosphere, which natural processes can no longer fully sequester to offset and prevent climate change. Increasing efforts have been focused on utilizing proteins from photosynthetic microorganisms for solar energy capture. We use sortase-mediated ligation to attach the Photosystem I (PSI) complex from Synechocystis sp. PCC 6803 in a preferential orientation to direct electron flow to a conductive gold surface, thereby enhancing current production when converting solar energy into electrical energy by. Sortase A is an enzyme found in Gram-postive bacteria that recognizes substrates containing an LPXTG sequence and catalyzes the cleavage of the amide bond between the threonine and the glycine, generating a thioester intermediate. The thioester intermediate undergoes nucleophilic attack by an amino group of an amino-terminated (Gly)3-decorated gold surface. We have engineered a stromal subunit, near the iron-sulfur clusters, of PSI to contain the LPXTG-sortase recognition sequence on exposed C-termini for uniform orientation for electron transfer. Our current work has shown that using this attachment scheme will produce currents on the 150-250 nA/cm^2 range. When using a reduced redox mediator, compared to an oxidized species, we get 10 times more current density suggesting using sortase-mediated ligation aids in uniform orientation of PSI at the surface.