Jeffrey Warren

Assistant Professor

Education

  • B.Sc. - Washington State University (2005)
  • Ph.D. - University of Washington (2010)
  • Postdoctoral Fellow - California Institute of Technology

Research

Protein-Modified Indium Tin Oxide Photoelectrochemical Devices

Capture and conversion of energy from sunlight is the most promising way to meet growing global energy demand. Interfacing light collection machinery with catalysts for fuel production or substrate modification is highly desirable. Few catalysts are as selective as proteins and new applications continue to emerge. We propose the development of photosensitizer-modified redox proteins that are attached to transparent conducting electrodes for use as photoelectrochemical catalysts. Our initial work focuses on functionalizing indium tin oxide(ITO)-coated glass and nano-ITO films with sensitizer-labeled proteins whose intramolecular electron transfer (ET) reactivity is established. These studies provide a framework for critical evaluation of protein surface coverage, protein orientation, electron transfer kinetics, and performance and efficiency. Efforts will turn toward nanoITO devices functionalized with cytochrome P450s for hydrocarbon oxidation and hydrogenase for H+ reduction (H2 evolution). The ultimate goal is to produce robust and efficient photoelectrochemical devices that exploit Nature’s catalysts.

 

Modifed Redox Proteins for Biopolymer Degradation

The biopolymer lignin is naturally digested under ambient conditions by lignin peroxidases (LiPs), a transformation that would be of great use on an industrial scale. Application of LiPs on large scales is hampered by low yielding LiP expression. We are developing cytochrome c peroxidase (CcP)-based analogs of LiPs; the two enzymes show similar tertiary structure, but standard CcP expressions yield large amounts of soluble protein. Modified CcP enzymes will be obtained from the introduction of a handful of known mutations, as well as of the catalytic surface tryptophan that is the unique site of radical reactivity in LiPs. We will explore heme redox chemistry and reactions with organic models and with natural lignin. We also are exploring rapid purification techniques and investigating catalysis using crude or partially purified cell lysates. These scaffolds provide the opportunity to study the formation and reactivity of biologically important amino acid radicals. We will investigate practical application in lignin digestion or treatment of waters contaminated with organic material.

Tuning Redox Reactivity in Modified Metalloproteins

Enzymes tune metal ion reduction potentials over a range of >1 V and catalyze an array of challenging redox transformations. We will investigate the redox properties and chemical reactivity of modified proteins with transition metals constrained in frustrated geometries. We take a page from small molecule inorganic chemistry and envision our protein scaffolds as “ligands.” We first focus on three metalloproteins to assess tractability. The most noteworthy scaffolds will be culled for thorough investigation. Our initial efforts focus on three proteins: Cu-containing rusticyanin from Tferrooxidans, [FeS]-containing rubredoxin from P. furiosus, and heme-containing cytochrome c from yeast, all of which are simple to express, tolerate a variety of mutations, and all can be crystallographically characterized. Select Cu-ligating amino acids in wild-type rusticyanin will be replaced with hard ligands and other outer sphere ligands will be modified. Reactivity of Fe, Co, and Cu proteins will be explored. Outer-sphere tuning will be explored in Fe(cysteine)4 and FeOH(cysteine)3 rubredoxins. Emphasis will be placed on frustrated coordination geometries in Ni and Fe proteins. Finally, the heme-pocket in c-type cytochromes will be explored, including reduction potential tuning and reactivity with substrates such as O2, NOX, and ClO2.

Publications

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Courses

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