Investigator: Christopher Reid, Bryant University

Scientific Theme: Molecular Toxicology

Abstract: The microbial glycome contains numerous attractive targets for antibiotic discovery. The mesh-like heteropolymer that surrounds all bacterial cells (with the exception of the mycoplasma), peptidoglycan (PG), confers strength, support, and shape to bacteria, as well as resistance to internal turgor pressure. Maintaining the integrity of PG is essential to bacterial viability, which is reflected by the number of different classes of clinically important antibiotics that target its biosynthesis. The PG sacculus is composed of the amino sugars N-acetylglucosamine (GlcNAc) and N-acetyl muramic acid (MurNAc), linked via a beta-(1,4)- glycosidic linkage.(4) Attached to the C-3 lactyl moiety of MurNAc is a highly variable penta-peptide composed of alternating L- and D- amino acids. Adjacent glycan strands are inter-connected through cross-links between these peptides. The biosynthesis of PG, particularly the cytoplasmic assembly and periplasmic cross-linking steps is fairly well understood. Some of the most successful antibiotics to date, including the beta-lactams and vancomycin, inhibit enzymes involved in PG biosynthesis. Conversely, remodeling of PG by glycosidases and lyases is poorly understood despite the important roles of these enzymes in cell growth and division.(5) Many current cell wall acting antibiotics are plagued by resistance issues. In order for the cell wall to continue to be a source of antimicrobial targets, exploitation of the enzymes that act on the invariable glycan backbone is essential. We have identified novel Ugi-derived terminal alkynes that show potent activity against Gram-positive pathogens. This project will evaluate these compounds against a suite of important pathogens (S. aureus, C. difficile, S. pneumoniae etc) for effectiveness. The interaction between the inhibitors and the putative molecular target, LytG an N-acetylglucosaminidase from B. subtilis will be characterized biochemically. Additionally, we will investigate these molecules as potential chemical probes for studying bacterial cell wall metabolism.

Human Health Relevance: This project will evaluate novel chemical entities for antibacterial activity. These compounds may serve as a new approach to targeting the bacterial cell wall. Our understanding of bacterial cell wall metabolism, in particular how it is regulated is poorly understood. We plan to evaluate these Ugi-derived terminal alkynes as chemical probes to study this essential bacterial process.