Abstract
We are designing and testing entirely novel photochemical proteins to be incorporated into the genome of living cells to provide a self-sustaining way to convert solar energy into useful chemical fuels. By intercepting light energy and initiating charge separation from the excited singlet state, while avoiding competing functions normal to natural photo-systems, these manmade photochemical proteins promise maximized engineering efficiencies solely directed to fuel production. We design these simply folded, light and redox active cofactor binding proteins, called maquettes, to meet photochemical requirements in the aqueous compartments of the cell. This simplifies expression, assembly, transport, and future catalytic steps of fuel production, ideally using water as a source of electrons. Maquette design applies first principles of protein folding and cofactor assembly, with cofactor placement inspired by natural protein engineering. The creation of an oxygen transport maquette analogous to the hemoglobins, but without any sequence or fold similarity, is proof that a basic understanding of mechanistic engineering in complex natural proteins can clear the way to functional reproduction in simply designed maquettes. We are now applying first-principles molecular electron tunneling engineering drawn from a collective assessment of natural photo-systems.
This elementary molecular engineering of solar energy conversion we have revealed removes many difficulties in the construction of photochemical maquettes working in living microorganisms. While there are significant hurdles still to surmount, early developments are promising. A wide variety of maquettes are readily expressed in high, scalable yield. Maquettes integrate with the in vivo machinery of cofactor biogenesis and ligation of bilins, hemes and chlorophyll. They are compatible with membrane transport by either Tat or Sec transporters. Maquettes have also been fused with natural light-harvesting proteins (biliproteins) to support multi-cofactor light energy transport.
