Differentiating the Two Complementary Flavins in a Bifurcating Electron Transfer Flavoprotein

University Of Kentucky Research Foundation, Lexington KY

Investigators

Abstract

With support from the Chemistry of Life Processes Program in the Division of Chemistry, Professor Anne-Frances Miller and her team at the University of Kentucky are examining how bacteria have managed to optimize their energy efficiency. Science has advanced to the point that it is now possible to supply all the energy needed by mankind, from wind and sunlight. However, these are intermittent, low-density sources that need to be 'stepped up' to power appliances such as hair driers. It turns out that bacteria possess enzymes capable of producing concentrated power from readily available fuel sources. These enzymes employ a mechanism wherein pairs of electrons are obtained from a cheap abundant fuel, but only one of the electrons is allowed to run 'down-hill'. The enzyme somehow harnesses this favorable process to drive an unfavorable 'up-hill' reaction that yields a much more potent electron carrier than the starting one. To enable design of materials able to do the same, the proposed research seeks to learn how nature does this. Flavin molecules related to the vitamin riboflavin, bound in proteins as cofactors are central to the mechanism. The planned research seeks to elucidate how the protein adjusts the flavin's reactivity. Flavins are yellow and fall into the larger chemical category of pigments. The broader impact of this work will be to develop a course for non-chemists that will employ fiber art and dyeing activities to explain core chemical concepts. This hands-on learning approach is designed to reach audiences who do not find book- and lecture-based courses compelling. Thus, the proposed work aims to engage a larger audience in the fun and curiosity of chemistry, and to harness chemistry in larger service to society. This research seeks to learn how bifurcating electron transfer flavoproteins (ETFs) tune the reactivities of their two flavins to cause one flavin to execute single electron transfers only, but the other flavin to have a very high energy semiquinone state that causes transfer of one electron to be tightly coupled to transfer of the second. A specific hypothesis is that the pyrophosphate group built into flavin adenine dinucleotide (FAD) could have agency in modulating the activity of the flavin. The proposed work also addresses the nature and lessons inherent in a novel state of the ETF that is proposed to involve cooperation of both flavins. The research integrates computational, spectroscopic, electrochemical, and biochemical strategies. To develop computational approaches and enable interpretation of flavin optical spectra in terms of underlying electronic structure and reactivity, a systematic approach is proposed, beginning with covalently modified flavins. Once validated, computational approaches would then be employed to infer the electronic perturbations produced by different protein sites in which flavins are bound. While flavin spectroscopy is at the center of the proposed research, the proposal exploits pigments more generally as vehicles to make core concepts of chemistry accessible to non-scientist audiences. A lab and lecture course on plant pigments in fiber arts will be developed into a modular on-line course, including guidance for hands-on activities. The team will assemble execution kits that rural schools or homeschoolers will be able to borrow, in order to follow along with recorded demonstrations and presentations. This approach seeks to overcome barriers that prevent many people from engaging with chemistry. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.