Glycans are ubiquitous and play important biological roles, yet chemical methods for probing their structure and function within cells remain limited. Strategies for studying other biomacromolecules, such as proteins, often exploit chemoselective reactions for covalent modification, capture, or imaging. Unlike amino acids that constitute proteins, glycan building blocks lack distinguishing reactivity because they are composed primarily of polyol isomers. Moreover, encoding glycan variants through genetic manipulation is complex. We therefore developed a new, generalizable strategy for chemoselective glycan modification that directly takes advantage of cellular glycosyltransferases. Many of these enzymes are selective for the products they generate yet promiscuous in their donor preferences. Thus, we designed reagents with bioorthogonal handles that function as glycosyltransferase substrate surrogates. In a previous study, we validated the feasibility of this approach by synthesizing and testing probes of D-arabinofuranose (D-Araf), a monosaccharide found in bacteria and an essential component of the cell wall that protects mycobacteria, including Mycobacterium tuberculosis (Mtb). The result is the first probe capable of selectively labeling arabinofuranose-containing glycans. Based on this precedent, this project aims to develop analogous probes of D-mannose (D-Man), which is a component of the lipoarabinomannan, an extracellular glycopolymer that has been shown to cause virulence in pathogenic Mtb. There are currently no chemical probes specific to this polysaccharide. This work demonstrates the generality of our biocatalytic labeling strategy as we can see specific labeling of distinct structures composed of unique monosaccharides. Our D-Man probes will provide insight into glycosyltransferase activity, distribution of cell wall components during mycobacterial cell growth, and changes in the cell wall of mycobacteria during macrophage infection.

Biosynthetic glycan labeling of the mycobacterial cell wall

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ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.