With this award, the Chemistry of Life Processes Program in the Chemistry Division is funding Professor Bridgette Barry at the Georgia Institute of Technology to investigate proton coupled electron transfer (PCET) reactions in the protein, ribonucleotide reductase (RNR). This enzyme speeds up the production of deoxyribonucleotides, which are building blocks of DNA, and thus plays a pivotal role in cell division. The deoxyribonucleotides are formed from ribonucleotides by a process that involves transfer of negatively-charged electrons over a long distance. The transfer of the electrons is coordinated with the transfer of positively-charged protons. Professor Barry studies how protein motions or dynamics facilitate and control these proton-coupled electron transfer (PCET) reactions in RNR. The intellectual merit of this project lies in the generation of fundamental chemical insights into PCET reactions, which are ubiquitous in biology. Professor Barry participates in a joint teaching and research effort in collaboration with Professor Lisa Hibbard at Spelman College, an Historically Black College or University (HBCU) for women. In addition, Dr. Barry is initiating a collaboration with the Center for the Visually Impaired in Atlanta to begin STEM tutoring of high school and middle school students with vision impairments. This effort serves as the basis for innovation in the freshman chemistry curriculum at Georgia Tech. The goal is to further and more broadly enhance the participation of visually impaired individuals in STEM disciplines.
This research project compares different members of the Class 1a RNR enzymes isolated from bacteria and human cells, with the goal of defining conserved PCET mechanism(s). Enzymes from this class are composed of two types of subunits, alpha and beta. They employ a tyrosyl radical (YO.)-diferric cofactor situated in the beta subunit as a radical initiator for substrate reduction in the alpha subunit. This process occurs through reversible PCET over a conserved pathway of tyrosine residues situated in the alpha and beta subunits. Remarkably, the radical transfer pathway spans 35 angstroms. Professor Barry tests the hypothesis that radical transfer across the alpha/beta interface changes the conformation of the YO. radical initiator, alters hydrogen bonding to YO. and the diferric cluster, and changes the conformation and hydrogen bonding of other tyrosines on the PCET pathway. Two techniques, namely reaction-induced FT-IR (RIFT-IR) and UV resonance Raman (UVRR) spectroscopy,, are employed. The UVRR and RIFT-IR spectra are assigned by isotopic labeling, solvent isotope exchange, site-directed mutagenesis, and site-specific mutagenesis using unnatural amino acids. Spectral results are interpreted by comparison to Density Functional Theory (DFT) calculations on tyrosine-containing peptides and on models of the tyrosyl radical-differic cluster. Molecular dynamics simulations of the subunit in the tyrosyl radical and tyrosine singlet states are also used to simulate redox-linked conformational changes. This project advances the fundamental understanding of enzyme mechanism and aids in the development of biomimetic strategies for energy conversion.
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.
