Prof. Ian Wheeldon
Department of Chemical and Environmental Engineering
University of California, Riverside
Nature leverages substrate-mediated diffusion to facilitate and enhance enzyme catalysis. Two interesting and compelling examples are the enzyme superoxide dismutase (SOD) and the bifunctional enzyme thymidylate synthase-dihydrofolate reductase (TS-DHFR). SOD uses charge complementarity to produce substrate-enzyme interactions that enhance enzyme kinetics by directing the substrate to the enzyme’s active site. A positively charge patch on the surface TS-DHFR restricts diffusion of a negatively charged reaction intermediate to a pre-defined channel between two active sites, thus promoting substrate channeling and enhancing pathway catalysis. These are useful examples from which we can draw design inspiration for synthetic enzyme cascades with enhanced catalysis. To this end, our research group is designing new multienzyme complexes to study the effects of cascade structure (i.e., scaffold geometry and chemistry) on reaction kinetics. Our overall goal is to turn our understanding of these relationships into a generalized set of design rules that can be used to engineer optimized cascade catalysis. The first step of this work is to investigate interactions between multienzyme scaffolds and cascade substrates. The SOD and TS-DHFR examples suggest that substrate-scaffold interactions are important and can be beneficial to catalysis. Here, we demonstrate that DNA scaffolds can enhance the kinetics of assembled enzymes and that these enhancements are related to the binding energy of the substrate and DNA scaffold. We hypothesize that enhancement are due to an increase in local concentration of the substrate resulting from substrate-DNA interactions. We confirm this hypothesis by demonstrating control over the apparent Michaelis constant of enzyme-DNA nanostructures by tuning the interactions between substrates and DNA scaffold. These findings represent an important first step in designing multienzyme complexes and demonstrate that interactions between substrates and the scaffolds must be considered when engineering such structures.
Dr. Wheeldon is an Assistant Professor of Chemical and Environmental Engineering at the University of California, Riverside. He received his PhD in Chemical Engineering from Columbia University in 2009, and completed two years of postdoctoral training at Harvard Medical School and the Wyss Institute for Biologically Inspired Engineering at Harvard University. Dr. Wheeldon received a Master’s of Applied Science from the Royal Military College of Canada (2003), and a Bachelor’s of Applied Science (1999) from Queen’s University, Canada. His research is focused on protein and biomolecular engineering for biocatalysis and metabolic engineering.