PROJECT SUMMARY Microbial metabolic function and adaptability are important in many facets of human health and disease. This proposal centers on studies of the microbial metabolic enzyme 1-deoxy-D-xylulose 5-phosphate synthase (DXPS). DXPS catalyzes the thiamin diphosphate (ThDP)-dependent synthesis of the essential metabolite DXP, which is found in the gut microbiota, pathogenic bacteria and parasites, but not in humans. Positioned at a metabolic branchpoint, DXP serves as a precursor to indispensable isoprenoids and vitamins, thus, we postulate DXPS plays key roles in microbiome function and microbial metabolic adaptation. Our long-term goal is to learn how microbes use DXPS in different contexts, toward understanding its roles in the microbiome and its potential as an antimicrobial target. Our group discovered a unique ligand-gated mechanism used by DXPS that bestows targets for selective inhibition and may enable DXPS to sense and respond to its environment. The goals of this proposal are to dissect how DXPS responds to molecular cues, examine this sensing mechanism in different chemical contexts, and establish novel inhibition strategies that target this distinctive feature of DXPS. Insights gained from this research will direct our thinking about DXPS function, and guide development of chemical probes needed to study DXPS roles in microbes.