Event

Title "Looking to the future by modeling the past: Design and characterization of engineered metalloenzymes for small molecule activation

Abstract:

Nature has evolved diverse systems to carry out energy conversion reactions. Metalloenzymes such as hydrogenase, carbon monoxide dehydrogenase, acetyl coenzyme A synthase, and methane monooxygenase use earth-abundant transition metals such as nickel and iron to generate and oxidize small-molecule fuels such as hydrogen, carbon monoxide, acetate, and methane. These reactions are highly valuable to understand and harness in the context of the impending global energy and climate crisis. However, the native enzymes are costly to isolate, sensitive to external conditions, and generally poorly suited for large-scale application. To address these limitations, we have pursued two distinct metalloprotein engineering approaches.

In the first, robust scaffolds such as azurin and rubredoxin have been converted into model systems that mimic the structure and function of complex nickel metalloenzymes. By introducing non-native metals and redesigning the primary and secondary coordination spheres, we have installed novel activity into these simple electron transfer proteins, including catalytic hydrogen evolution and carbon dioxide fixation. Adding key elements from the secondary and tertiary coordination spheres of hydrogenase and CODH enhances both activity and selectivity, pointing to functional roles of specific residues within the natural enzymes.

Accomplishing selective C-H bond activation using oxygen, analogous to the reaction performed by methane monooxygenase, poses a complementary challenge. The R2-like ligand-binding oxidase (R2lox) proteins represent a new class of redox-active Mn/Fe proteins, defying the Irving Williams series to assemble a heterobimetallic core. Upon O2 activation, R2lox is capable of executing multi-electron chemistry, catalyzing C-H bond activation to generate an unprecedented tyrosine-valine crosslink. Given the pervasive structural similarities between R2lox and the diiron methane monooxygenase, R2lox presents a unique opportunity for investigating the fundamental chemistry of this novel Mn/Fe cofactor, offering a scaffold within which to modulate and develop increasingly potent reactivity.

Steady-state and time-resolved optical, vibrational, and magnetic resonance spectroscopic techniques have been used in conjunction with bioanalytical methods and calculations to probe the active-site structures across different states and determine the catalytic mechanisms. These findings will be discussed in the context of identifying the fundamental principles underlying highly active native enzymes and applying those principles towards engineering effective model metalloproteins for energy conversion reactions.

Bio:

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. Recently, the group has 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.