Lectin-mediated adhesion: Testing of tailor-made cellulose derivatives with ConA and live E. coli bacteria

Due to the high exigence for treatment of bacterial infections, anti-adhesion therapy has emerged as an alternative method in an era of antibiotic resistance. Here, we have conjugated azido-functionalized cellulose with specific carbohydrate ligands (mannose and glucose, respectively) via copper-catalyzed azide-alkyne click chemistry (CuAAC) resulting in homo- and hetero-glycosylated cellulose derivatives with a DS > 0.9. The new materials, CellulMan and CellulManGlc, were evaluated as potential anti-adhesive reagents with type 1-fimbriated E. coli bacteria and additionally with the plant lectin Concanavalin A (ConA). We have determined the adhesion properties of the new glycopolymers as well as their agglutination behavior in an in-depth study combining two- and three-dimensional assays. The tested synthetic glycopolymers differ in their biological behavior as lectin ligands depending on the respective glycodecoration. In particular, CellulMan shows a remarkably low minimal effective concentration cmin ≤ 2 pg/mL as adhesive material with E. coli. Overall, the assays demonstrate that glyco-modified cellulose serves as an excellent antiadhesive as well as adhesive surface material for both type 1 fimbriated E. coli and ConA, being superior to natural polysaccharides.

Orthogonal photoswitching of heterobivalent azobenzene glycoclusters: the effect of glycoligand orientation in bacterial adhesion

Carbohydrate recognition is fundamental to a plethora of cellular processes and hence the elucidation of the structural determinants of the recognition process is a prerequisite for understanding and manipulating carbohydrate-protein interactions, such as in the inhibition of carbohydrate-specific bacterial adhesion. For receptor binding, glycoligands have to be properly oriented in three-dimensional space and additionally, secondary interactions exerted by multivalent glycoligands have an effect on affinity. A recently introduced orthogonally photoswitchable heterobivalent azobenzene Glc/Man glycocluster was utilized to examine these aspects of carbohydrate recognition in a bacterial adhesion-inhibition assay. The measured results were systematically contextualized employing new reference compounds such as the respective homobivalent Man/Man glycocluster. An in-depth study comprising the analysis of the photochromic properties and the potential as inhibitors of bacterial adhesion of the synthetic glycophotoswitches in their different isomeric states led to new insights into the role of ligand orientation in carbohydrate recognition. The experimental results were underpinned by molecular modeling.

Advancing Optoglycomics: Two Orthogonal Azobenzene Glycoside Antennas in One Glycocluster-Synthesis, Switching Cycles, Kinetics and Molecular Dynamics

Carbohydrate recognition is essential for numerous biological processes and is governed by various factors within the supramolecular environment of the cell. Photoswitchable glycoconjugates have proven as valuable tools for the investigation and modulation of carbohydrate recognition as they allow to control the relative orientation of sugar ligands by light. In order to advance the possibilities of such an "optoglycomics" approach for the glycosciences, we have synthesized a biantennary glycocluster in which two glycoazobenzene antennas are conjugated to the 3- and 6-position of a scaffold glycoside. Orthogonal isomerization of the photoswitchable units was made possible by the different conjugation of the azobenzene moieties via an oxygen and a sulfur atom, respectively, and the ortho-fluorination of one of the azobenzene units. This design enabled a switching cycle comprising the EE, EZ and the ZZ isomer. This is the first example of an orthogonally photoswitchable glycocluster. The full analysis of its photochromic properties included the investigation of the isolated glycoazobenzene antennas allowing the comparison of the intra- versus the intermolecular orthogonal photoswitching. The kinetics of the thermal relaxation were analyzed in detail. A molecular dynamics study shows that indeed, the relative orientation of the glycoantennas and the distances between the terminal sugar ligands significantly vary depending on the isomeric state, as intended.

Synthesis of regioisomeric maltose-based Man/Glc glycoclusters to control glycoligand presentation in 3D space

The investigation of carbohydrate recognition in a natural environment suffers from the complexity of overlapping functional effects such as multivalency and heteromultivalency effects. Another key factor in carbohydrate recognition is the presentation mode of glycoligands in three-dimensional (3D) space. In order to trace out the effect of 3D ligand presentation, we utilized an oligosaccharide model to precisely control the spatial relation between a mannose ligand (Man) and a glucose moiety (Glc). A disaccharide (maltose) served as a scaffold to alternately conjugate Man and Glc at position 6 and 6' of a synthetic maltoside, resulting in a pair of regioisomeric heterobivalent glycoclusters. The biological effect of this specific structural tuning was tested in a native system employing mannose-specific adhesion of live E. coli cells. Indeed, the variable 3D presentation of the Man ligand resulted in a 2-fold difference between the regioisomeric heterobivalent glycoclusters as inhibitors of bacterial adhesion. This can be considered a remarkable effect, which could be interpreted by computer-aided modelling of the complexes between the bacterial lectin and the synthetic regioisomeric glycoligands.

Automated Quantification of Hydroxyl Reactivities: Prediction of Glycosylation Reactions

The stereoselectivity and yield in glycosylation reactions are paramount but unpredictable. We have developed a database of acceptor nucleophilic constants (Aka) to quantify the nucleophilicity of hydroxyl groups in glycosylation influenced by the steric, electronic and structural effects, providing a connection between experiments and computer algorithms. The subtle reactivity differences among the hydroxyl groups on various carbohydrate molecules can be defined by Aka, which is easily accessible by a simple and convenient automation system to assure high reproducibility and accuracy. A diverse range of glycosylation donors and acceptors with well-defined reactivity and promoters were organized and processed by the designed software program "GlycoComputer" for prediction of glycosylation reactions without involving sophisticated computational processing. The importance of Aka was further verified by random forest algorithm, and the applicability was tested by the synthesis of a Lewis A skeleton to show that the stereoselectivity and yield can be accurately estimated.

Multivalent glycoligands with lectin/enzyme dual specificity: self-deliverable glycosidase regulators

Multivalent mannosides with inherent macrophage recognition abilities, built on β-cyclodextrin, RAFT cyclopeptide or peptide dendrimer cores, trigger selective inhibition of lysosomal β-glucocerebrosidase or α-mannosidase depending on valency and topology, offering new opportunities in multitargeted drug design.