Raquel L. Lieberman is the recipient of the 2017 Georgia Tech Sigma Xi Best Faculty Paper Award. Lieberman is an associate professor in the School of Chemistry and Biochemistry. The paper recognized by this award is “Enzymatic hydrolysis by transition-metal-dependent nucleophilic aromatic substitution,” published in Nature Chemical Biology.
The work involves protein crystallography, enzymology, and organic chemistry to address a question related to chemical ecology. This diversity of fields exemplifies the highly interdisciplinary questions Georgia Tech researchers are aiming to answer.
Also notable is the diversity of Lieberman’s research team. It involved high school, undergraduate, and graduate students; a technician; and a postdoctoral fellow. Also with the team was a remarkable high school teacher whose teaching has been transformed by doing research in the Lieberman lab. The paper uniquely embodies Georgia Tech’s motto: Progress and Service.
The paper describes a precedent-setting metalloenzyme discovered in the context of the complex biochemical warfare waged in farm soils where potato is grown. In such soils, the bacterium Streptomyces scabies infects potato tubers and secretes compounds that induce the formation of scabs; among them is 5-nitroanthranilic acid (5NAA).
Also in the same soils is another bacterium, Bradhyrhizobium sp. This nonpathogenic microbe seems to defend itself and the potato plant from S. scabies by detoxifying 5NAA. Lieberman’s collaborator of more than five years, Jim C. Spain, in the School of Civil and Environmental Engineering, discovered the unusual metalloenzyme in this bacterium.
The enzyme – 5-nitroanthranilic acid aminohydrolase (5NAA-A) – performs unusual chemistry: hydrolysis of a nitroaromatic compound. Nitroaromatic compounds are notoriously toxic, challenging to synthesize, and difficult to degrade, but are found widely in synthetic dyes, explosives, and pesticides.
The Lieberman team solved the structure of 5NAA-A and investigated its enzyme mechanism, substrate specificity, metal-binding properties, and phylogeny. They found that the chemistry it mediates, and the mechanism it uses, is rare among known enzymes.
A major force in the work was Casey Bethel, who is Georgia’s 2017 Teacher of the Year (TOTY). Bethel helped pave the way to solving the crystal structures of 5-NAA-A and mentored students who helped confirm its unique chemical properties.
A highly charismatic high school teacher, Bethel has spent the past six summers working in the Lieberman lab. His participation was made possible by Georgia Intern Fellowships for Teachers (GIFT), a program administered by the Center for Education Integrating Science, Mathematics, and Computing. Funds from Lieberman’s NSF CAREER award sponsored Bethel for four of the six years.
“It’s rare – we believe unprecedented! – in Georgia for the TOTY award to go to a STEM teacher at the high school level,” Lieberman says.
“On behalf of my co-authors, I thank Sigma Xi and Georgia Tech for this honor,” Lieberman says. “Not only does our discovery have impact from a number of scientific angles; our study also truly epitomizes the interdisciplinary and collaborative culture at Georgia Tech."