Georgia Institute of Technology

Research in my group is focused on how the dynamic and responsive protein matrix facilitates biological catalysis.  We use a wide range of high resolution spectroscopic, biochemical, and structural techniques to describe the reaction coordinate, which reveals the motion of the protein in space and time.  We test the design principles, which we uncover, by building biomimetic models.

Photosynthetic water oxidation and solar energy conversion.  Photosystem II uses light energy to oxidize water, producing molecular oxygen. The reaction is catalyzed at a Mn4CaO5 cluster using a photo-generated tyrosyl radical.  We are studying the catalytic steps of this reaction using resonance Raman, FT-IR, and EPR spectroscopies. We have developed a method to incorporate unnatural amino acid residues into the oxygen-evolving center. Noncanonical amino acid residues provide unique spectroscopic tools.  Elucidation of the water oxidizing mechanism will contribute to new developments in solar energy conversion.

Biomimetic peptide models.   Biological proton coupled electron transfer reactions are subjected to exquisite control over direction and kinetics; these mechanisms are not yet understood.  We seek to assemble nanoscale, peptide-based devices, which can carry out similar reactions.  These maquettes (or models) will provide water-soluble, stable redox agents with tunable redox potentials, kinetics, and directional control of charge transfer. These efforts will produce prototypes, which will generate new insights into important biological reactions, such as photosynthesis and DNA synthesis.  We have succeeded in engineered a robust photosystem II-inspired scaffold, which exhibits a proton coupled electron transfer reaction.

Proton coupled electron transfer and DNA synthesis.  Ribonucleotide reductase catalyzes the production of deoxyribonucleotides in all cells.  Ribonucleotide reductase is the target of anti-cancer therapeutics.  This protein uses a tyrosyl radical-diferric cofactor as a radical initiator.  We seek to understand how the oxidizing power of the intermediary tyrosyl free radical is controlled. This research project, using reaction-induced FT-IR spectroscopy, gives a picture of the movements of the electron and proton and describes the protein conformational landscape associated with the transfer.  Elucidation of these mechanisms will contribute to the design of more effective cancer therapeutic agents.