Fullerene‐sp²‐Iminosugar Balls as Multimodal Ligands for Lectins and Glycosidases: A Mechanistic Hypothesis for the Inhibitory Multivalent Effect

Abstract

Concerted functioning of lectins and carbohydrate‐processing enzymes, mainly glycosidases, is essential in maintaining life. It was commonly assumed that the mechanisms by which each class of protein recognizes their cognate sugar partners are intrinsically different: multivalency is a characteristic feature of carbohydrate–lectin interactions, whereas glycosidases bind to their substrates or substrate‐analogue inhibitors in monovalent form. Recent observations on the glycosidase inhibitory potential of multivalent glycomimetics have questioned this paradigm and led to postulate an inhibitory multivalent effect. Here the mechanisms at the origin of this phenomenon have been investigated. A D‐gluco‐configured sp2‐iminosugar glycomimetic motif, namely 1‐amino‐5N,6O‐oxomethylydenenojirimycin (1N‐ONJ), behaving, simultaneously, as a ligand of peanut agglutinin (PNA) lectin and as an inhibitor of several glycosidases, has been identified. Both the 1N‐ONJ–lectin‐ and 1N‐ONJ–glycosidase‐recognition processes have been found to be sensitive to multivalency, which has been exploited in the design of a lectin–glycosidase competitive assay to explore the implication of catalytic and non‐glycone sites in enzyme binding. A set of isotropic dodecavalent C60‐fullerene–sp2‐iminosugar balls incorporating matching or mismatching motifs towards several glycosidases (inhitopes) was synthesized for that purpose, thereby preventing differences in binding modes arising from orientational preferences. The data supports that: 1) multivalency allows modulating the affinity and selectivity of a given inhitope towards glycosidases; 2) multivalent presentation can switch on the inhibitory capacity for some inhitope–glycosidase pairs, and 3) interactions of the multivalent inhibitors with non‐glycone sites is critical for glycosidase recognition. The ensemble of results point to a shift in the binding mode on going from monovalent to multivalent systems: in the first case a typical ′′key–lock′′ model involving, essentially, the high‐affinity active site can be assumed, whereas in the second, a lectin‐like behavior implying low‐affinity non‐glycone sites probably operates. The differences in responsiveness to multivalency for different glycosidases can then be rationalized in terms of the structure and accessibility of the corresponding carbohydrate‐binding regions.

Synthesis of giant globular multivalent glycofullerenes as potent inhibitors in a model of Ebola virus infection

“…Depending upon the starting sugar derivatives employed (monomer, dimer or trimer) 12, 24 and up to 36 monosaccharides have been introduced on the periphery of the fullerene central core in a straightforward manner. 14,15,16,17 Remarkably, some of the aforementioned glycofullerenes have proven to show interesting biomedical applications. 18 Thus, a significant multivalent effect has been observed in the inhibition profile of a [60]fullerene hexakis-adduct endowed with 12 iminosugar units towards different glycosidases.…”

“…18 Thus, a significant multivalent effect has been observed in the inhibition profile of a [60]fullerene hexakis-adduct endowed with 12 iminosugar units towards different glycosidases. 16 On the other hand, fullerene hexakis-adducts bearing 12 mannoses on the periphery behave as inhibitors of FimH, a bacterial adhesin. 19 Furthermore, studies carried out on hexakis-adducts of [60]fullerene endowed with 12, 24 and 36 mannoses have shown a multivalent effect in the interaction with Concanavalin A, 15 and acting as efficient inhibitors of cell infection by Ebola pseudotyped viral particles.…”

Biological applications of hydrophilic C60 derivatives (hC60s)− a structural perspective

“…On the contrary, other glycosidases, maltase, isomaltase and β-glucase, bore the deep and narrow active sites. Monosaccharides were more efficient than the multivalent system [89,90]. The similar multivalent system, C60 conjugating with 36 mannoses through long linkers, inhibited pseudotyped Ebola virus to enter into cells.…”

The Impact of Copper‐Catalyzed Alkyne–Azide 1,3‐Dipolar Cycloaddition in Fullerene Chemistry

“…[70][71][72] For example, the inhibition profile of fullerene hexakis-adduct 54, decorated with 12 iminosugar residues, was systematically evaluated towards various glycosidases. [70] Remarkably, significant multivalent effects were evidenced for the first time.…”