Research Interests
One of our major research areas is centered around microorganisms that produce secondary metabolites or natural products. These compounds find widespread use including antibiotics, immunosuppressants, anticancer agents, and antiparasitic agents. The carbon skeleton core of many of these compounds are produced by polyketide synthases (PKSs). We are studying these complex fascinating biosynthetic processes at both the genetic and enzymatic level. A combination of genetic techniques, including molecular breeding and in vivo recombination, are being used to generate engineered microorganisms in which the natural biosynthetic process of interest has been diverted, in some cases through the use of catalytically efficient hybrid PKSs. In combination with chemoenzymatic approaches and precursor-directed mutasynthesis we are producing a wide range of new natural products with a variety of biological activities.
Currently we are interested in the phoslactomycin (PLMs) and fostriecin (compounds with antitumor and antifungal activity), hygromycin A and pikromycin (antibacterial activity) and prodiginines (compounds with interesting immunosuppressant, antimalarial and antitumor activities). We have been able to generate a library of more than 50 new phoslactomycins and are evaluating their biological activities. We have also discovered that the prodiginines are orally effective in the treatment of malaria in mice.
We also study the primary metabolic pathways which provide the necessary precursors for assembling natural products. We have shown that manipulation of these processes affect the ratio and yields of natural product in a fermentation process. Currently we are both deciphering the importance of competing precursor pathways in mutagenized industrial strains under fermentation conditions which produce high titers of the natural product. We are also utilizing these strains as super hosts for heterologous expression of natural product biosynthetic processes where fermentation yields from the native microorganism are a limiting factor.
Our second area of research interests is the pathway of plant and bacterial fatty acid biosynthesis, catalyzed by type II fatty acid synthases (FASs). The unique features of this pathway, and of enzyme specific to this process have attracted considerable interest as both targets for both antibiotic development and biofuel production in bacteria and transgenic plants. 3-Ketoacyl ACP synthase III (KASIII) initiates fatty acid biosynthesis in this process by catalyzing a condensation between an acyl CoA and a malonyl ACP substrate. We are actively investigating different KASIII enzymes from Staphylococci aureus, Escherichia coli, and Mycobacterium tuberculosis (the organism that causes tuberculosis) and Plasmodial falciparum (the parasite responsible for malaria). We are using mutagenesis, molecular modeling, kinetic analyses and X-ray diffraction to probe the mechanism and varying substrate specificities of these enzymes. We have crystallized and solved the structure of the M. tuberculosis KASIII, believed to play a critical role in initiating mycolate biosynthesis in this pathogenic microorganism. We have designed and synthesized several series of selective synthetic KASIII inhibitors and are using techniques such as molecular modeling and X-ray crystallography with a long term goal of developing these into a new generation of antimalarial, antibacterial and antituberculosis drugs.