Our research focuses on mechanistic and structural studies of enzymes involved in the bacterial catabolism of aromatic and halogenated compounds. The specific enzymes examined under study are found in the tautomerase superfamily and the fumarylacetoacetate hydrolase (FAH) superfamily. In addition to advancing our general understanding of enzyme mechanisms, these studies provide insight into how enzymes evolve and how new activities emerge. It has become incumbent upon us to understand this process due to the ever-increasing prevalence of antibiotic-resistant bacteria and other drug-resistant organisms such as M. tuberculosis. Although there are several strategies for overcoming resistance (synthesis of new compounds, identification of new targets, inhibition of enzymes conferring resistance), a better understanding of how these new activities evolve in the first place might suggest some alternative and more effective approaches.
These studies have led us in a number of different directions. Most recently, for example, we have identified a tautomerase superfamily member (designated TomN) in a biosynthetic pathway for one ring of the anti-tumor, tomaymycin. Tomaymycin is one of the pyrrolo[1,4]benzodiazepine natural products that includes anthramycin and sibiromycin. The C ring of tomaymycin is generated in five enzyme-catalyzed steps from L-tyrosine. The genes encoding these enzymes have recently been cloned and their functions tentatively assigned, but there is limited biochemical evidence supporting the assignments of the last three steps. We are currently characterizing the enzymatic and non-enzymatic chemistry in the pathway. The ultimate goal is to use these enzymes to generate new, more potent tomaymycin analogues that are synthetically inaccessible.