UC Irvine

Production of platform and specialty chemicals is an ever-growing industry, but overreliance on renewable resources places a finite lifespan on many chemical processes. Industrial biocatalysis – using biological cells and or enzymes to drive chemical reactions – offers a more renewable alternative to many of these traditional processes. However, widespread adoption of biocatalysis is limited by the difficulty with maintaining precise control over reaction flux and directionality without significant unwanted side reactions. This often leads to the necessity of prohibitively costly purification and/or preparation steps that limit the applicability of these systems.Among the most essential simple chemical reaction steps necessary for a complete circular bioeconomy that often experience this issue is the interconversion between carbon redox states, particularly carboxylic acids, aldehydes, and alcohols. Carboxylic acids represent cheap, stable chemicals that are often discarded due to the cost typically associated with their reduction toward more valuable aldehydes or alcohols. Aldehydes represent an extremely attractive product class, as they are relatively reactive as precursors for more complex molecules such as pharmaceuticals. They also exhibit strong flavor and fragrance qualities that often result in their inclusion as flavor and/or fragrance agents or necessitating their removal if those qualities are considered undesirable. Similarly, alcohols can be employed as valuable precursors directly for many industries, or as aldehyde precursors due to their increased stability compared to aldehydes, relative ease of oxidation toward aldehydes.This work focuses on harnessing redox biocatalysis to interconvert these three carbon redox states. First, I detail how alcohol dehydrogenases can be engineered for improved noncanonical redox cofactor (NRC) activity, which allows for increased control over reaction thermodynamics, direction, flux, and cost when converting between aldehydes and alcohols. I will then detail ongoing work to attempt to elucidate a sequence- or structure-based motif that allows for these enzymes to naturally accept noncanonical redox cofactors. I will then discuss the characterization of several aldehyde dehydrogenases for aldehyde-carboxylic acid interconversion using NRCs and future work in our lab planned to expand on and engineer this activity for improvement. Finally, I will discuss the adaptation of the recently developed reverse aldehyde oxidation system (rAOX) to reduce carboxylic acids to aldehydes, alcohols, and other products using redox cofactors alone and our future plans for developing a platform to employ NRCs for carboxylic acid reduction.Together, this work advances the understanding and ability to control the interconversion of different carbon redox states in biocatalysis, laying the groundwork to continue engineering and elucidating understanding of multiple classes of enzymes that can be engineered to harness NRCs for sustainable biochemical production. More broadly, these efforts lay the foundation for a modular biocatalytic toolkit in which facile, well-understood cofactor engineering serves as a generalizable strategy for tuning control over redox reactions across a multitude of enzyme classes involved in newly emerging biocatalytic processes.