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Understanding Bioinorganic Reactivity Through the Lens of Electronic Structure
Presented by Prof. Hannah Shafaat
Hosted by Prof. Parkin
Metalloproteins perform the most challenging chemical reactions known, from carbon dioxide reduction to nitrogen fixation to water oxidation, using only earth-abundant transition metals while operating under mild conditions. To carry out such difficult processes, metal-containing active sites are placed within carefully constructed protein scaffolds, which provide precise secondary sphere interactions, long range electrostatics, and aqueous solvation environments. Extensive studies on naturally occurring metalloenzymes have shown that making changes at any level of the protein structure can substantially impact activity. However, synergistic or anti-cooperative effects can obscure the specific function of each metalloprotein element. To gain molecular-level understanding, we are developing protein-based models as structural, functional, and mechanistic mimics of naturally occurring metalloenzymes, taking advantage of the different layers of control that a protein scaffold inherently offers. Our targets include systems relevant to energy conversion, such as hydrogenase, carbon monoxide dehydrogenase (CODH), and acetyl coenzyme A synthase (ACS), as well as secondary metabolic processes, such as those carried out by members of the ferritin-like superfamily. By combining functional studies of our model proteins with diverse spectroscopic techniques and computational investigations, we can obtain a comprehensive understanding of how the electronic structure dictates reactivity in each system. In this presentation, I will describe recent results from our lab demonstrating how changes in the primary coordination sphere are used to understand changes in reactivity and perturbations to the catalytic mechanism(s). Ongoing efforts to systematically modulate and quantify the impact of the secondary and outer coordination environments will be discussed. Reconstructing functional metalloenzymes “from the ground up” offers direct insight into the fundamental chemical principles driving the natural systems.
Hannah received her B.S. in Chemistry from the California Institute of Technology (Caltech) in 2006, where she performed research on spectroscopic endospore viability assays with Adrian Ponce (NASA Jet Propulsion Laboratory) and Harry Gray. She received her Ph.D. in Physical Chemistry from the University of California, San Diego (UCSD) in 2011, under the direction of Professor Judy Kim, as an NSF Graduate Research Fellow and a National Defense Science and Engineering Graduate Fellow. During her graduate research, she used many different types of spectroscopy to study the structure and dynamics of amino acid radical intermediates in biological electron transfer reactions. After earning her Ph.D., Hannah moved across the ocean to Germany to study hydrogenase and oxidase enzymes and learn advanced EPR techniques as a Humboldt Foundation Postdoctoral Fellow working under Director Wolfgang Lubitz at the Max Planck Institute for Chemical Energy Conversion. Since starting her independent career, Hannah has received the NSF CAREER award in 2015 to support work on hydrogenase mimics, and in 2017, she was awarded the DOE Early Career award to support the group’s research on one-carbon activation in model nickel metalloenzymes. The group has also received support for their research on heterobimetallic Mn/Fe cofactors through the NIH R35 MIRA program for New and Early Stage Investigators. Hannah was also awarded the 2018 Sloan Research Fellowship.