Uncovering bacterial pseudaminylation with pan-specific antibody tools

Pseudaminic acids (Pse) are a family of carbohydrates found within bacterial lipopolysaccharides, capsular polysaccharides and glycoproteins that are critical for the virulence of human pathogens. However, a dearth of effective tools for detecting and enriching Pse has restricted study to only the most abundant Pse-containing glycoconjugates. Here we devise a synthesis of α- and β-O-pseudaminylated glycopeptides to generate 'pan-specific' monoclonal antibodies (mAbs) that recognize α- and β-configured Pse with diverse N7 acyl groups, as well as its C8 epimer (8ePse), presented within glycans or directly linked to polypeptide backbones. Structural characterization reveals the molecular basis of Pse recognition across a range of diverse chemical contexts. Using these mAbs, we establish a glycoproteomic workflow to map the Pse glycome of Helicobacter pylori, Campylobacter jejuni and Acinetobacter baumannii strains. Finally, we demonstrate that the mAbs recognize diverse capsule types in multidrug-resistant Acinetobacter baumannii and enhance phagocytosis to eliminate infections in mice.