Regioisomeric branched trisaccharides: a combined synthetic, biological, and computational approach to understand details of FimH-mediated bacterial adhesion

Abstract

Carbohydrate-mediated interactions are crucial in many biological processes, including microbial adhesion and infections, where glycan recognition is often governed by the three-dimensional presentation of saccharide ligands. In this study, we systematically explored how regioisomeric structural variations of a Glc/Man pair, scaffolded on various monosaccharides, influence the mannose-specific adhesion of E. coli bacteria which is mediated by the bacterial lectin FimH. A targeted synthetic library of di- and trisaccharides featuring α-D-mannopyranoside/β-D-glucopyranoside (Man/Glc) and Man/Man motifs was synthesized, focusing on variations of regio- and stereochemistry. These glycans were functionalized with anomeric azido groups allowing for an eventual conjugation. Screening of all saccharides in bacterial adhesion-inhibition assays using GFP-tagged type 1 fimbriated live E. coli revealed pronounced differences in inhibitory potencies which could be correlated with the specific spatial arrangement of the saccharide units, underscoring the significance of glycan topology in lectin recognition. Complementary molecular modeling provided a structure-based rationale for the observed structure–function relationships. This work highlights the critical role of three-dimensional glycan architecture in heteromultivalent carbohydrate recognition events.