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Homogeneous Glycoconjugate Produced by Combined Unnatural Amino Acid Incorporation and Click-Chemistry for Vaccine Purposes

Genetic code expansion is a powerful tool to introduce unnatural amino acids (UAAs) into proteins to modify their characteristics, to study or create new ...

Université de Nantes, CNRS, Unité Fonctionnalité et Ingénierie des Protéines (UFIP), UMR 6286

Galectins play key roles in numerous biological processes. Their mode of action depends on their localization which can be extracellular, cytoplasmic, or nuclear and is partly mediated through interactions with β-galactose containing glycans. Galectins have emerged as novel therapeutic targets notably for the treatment of inflammatory disorders and cancers. This has stimulated the design of carbohydrate-based inhibitors targeting the carbohydrate recognition domains (CRDs) of the galectins. Pursuing this approach, we reasoned that linear oligogalactosides obtained by straightforward iterative click chemistry could mimic poly-lactosamine motifs expressed at eukaryote cell surfaces which the extracellular form of galectin-3, a prominent member of the galectin family, specifically recognizes. Affinities toward galectin-3 consistently increased with the length of the representative oligogalactosides but without reaching that of oligo-lactosamines. Elucidation of the X-ray crystal structures of the galectin-3 CRD in complex with a synthesized di- and tri-galactoside confirmed that the compounds bind within the carbohydrate-binding site. The atomic structures revealed that binding interactions mainly occur with the galactose moiety at the non-reducing end, primarily with subsites C and D of the CRD, differing from oligo-lactosamine which bind more consistently across the whole groove formed by the five subsites (A-E) of the galectin-3 CRD.

Linear triazole-linked pseudo oligogalactosides as scaffolds for galectin inhibitor development.

Chemoenzymatic strategies are useful for providing both regio- and stereoselective access to bioactive oligosaccharides. We show herein that a glycosynthase mutant of a  α-glycosidase can react with unnatural glycosides such as 6-azido-6-deoxy-d-glucose/glucosamine to lead to β-d-galactopyranosyl-(1→3)-d-glucopyranoside or β-d-galactopyranosyl-(1→3)-2-acetamido-2-deoxy-d-glucopyranoside derivatives bearing a unique azide function. Taking advantage of the orthogonality between the azide and the hydroxyl functional groups, the former was next selectively reacted to give rise to a library of galectin-3 inhibitors. Combining enzyme substrate promiscuity and bioorthogonality thus appears as a powerful strategy to rapidly access to sugar-based ligands.

Christophe Dussouy

Université de Nantes, CNRS, Unité Fonctionnalité et Ingénierie des Protéines (UFIP), UMR 6286

Homogeneous Glycoconjugate Produced by Combined Unnatural Amino Acid Incorporation and Click-Chemistry for Vaccine Purposes