N-linked glycans are critical to the infection cycle of HIV, and most neutralizing antibodies target the high-mannose glycans found on the surface envelope glycoprotein-120 (gp-120). Carbohydrate-binding proteins, particularly mannose-binding lectins have also been shown to bind these glycans. Despite their therapeutic potency their ability to cause lymphocyte proliferation limits their application. In this study we report one such lectin named Horcolin (Hordeum vulgare lectin), seen to lack mitogenicity owing to the divergence in the residues at its carbohydrate-binding sites which makes it a promising candidate for exploration as an anti-HIV agent. Extensive ITC experiments reveal that the lectin was sensitive to the length and branching of mannooligosaccharides and thereby the total valency. Modeling and simulation studies demonstrate two distinct modes of binding, a monovalent binding to shorter saccharides and a bivalent mode for higher glycans, involving simultaneous interactions of multiple glycan arms with the primary carbohydrate binding sites. This multivalent mode of binding was further strengthened by interactions of core mannosyl residues with secondary conserved site on the protein, leading to an exponential increase in affinity. Finally, we confirmed the interaction of Horcolin with recombinant gp120 and gp140 with high affinity, and inhibition of HIV infection at nanomolar concentrations without mitogenicity.
Carbohydrate‐protein interactions define a multitude of cellular recognition events. We present herein synthetic glycovesicles as cell‐surface mimics in order to switch the nature of lectin recognition. The covalent glycovesicles, constituted with diacetylene monomers of various ligand densities at their surfaces, are prepared through photo‐polymerization. Vesicles with sparsely imbedded ligands engage in a lectin interaction leading to the formation of a dense, crosslinked multimeric complex. On the other hand, vesicles with many ligands, or completely covered with them, switch the lectin interaction to form a fully soluble monomeric complex, without crosslinking. Nanomolar dissociation constants govern these interactions, as assessed by a ligand‐displacement assay. The study demonstrates the switching nature – between monomeric and multimeric – of the interaction as a function of ligand density in the vesicles; the results are directly relevant to understanding such a phenomenon occurring at cell surfaces.
The derivatization of a polydiacetylene (PDA) polymer with free hydroxyl groups containing sugars leads to amphiphilicity of the polymer and the emergence of thermotropic liquid crystalline behavior, in addition to the thermochromatic properties. The diacetylene monomers, incorporated with mono‐ and disaccharides, exhibit mono‐ and/or enantiotropic phase behavior in a wide temperature range. Structural characterization and modeling studies reveal a lamellar arrangement and interdigitization of the molecules in the mesophase. The importance of the amphiphilicity as a source to induce mesomorphic behavior in PDA polymers is emphasized.
Glycovesicles mimic synthetic cell membrane surfaces and aid to delineate intricate, weak carbohydrate–protein interactions. In this report, the dependence of the hydrodynamic diameters in relation to the molar fractions of carbohydrate moieties in the mixed polydiacetylene (PDA) glycovesicles is evaluated. The glycovesicles are constituted with diacetylene monomers of varying molar fractions of carbohydrate moieties and the hydrodynamic diameters are assessed without and with polymerization of the vesicles. A strong dependence of the hydrodynamic diameter of glycovesicles is seen as a function of the molar fractions and the nature of the sugar moiety being either mono- or disaccharide. A monotonous increase in the hydrodynamic diameters of the glycovesicles occurs with the increase in mole fractions of the sugar monomer lipids. Upon polymerization, the hydrodynamic diameters reduce for the vesicles with lower mole fractions of sugar monomer, whereas the reverse occurs for glycovesicles possessing higher mole fractions. Disaccharide glycovesicles possess higher hydrodynamic diameters than monosaccharide-containing vesicles. Ligand–lectin interactions were probed with lactose disaccharide-containing glycovesicles with tetrameric peanut agglutinin lectin, from which an increase in the hydrodynamic diameters is observed, as the mole fraction of sugar monomer is increased in the PDA-glycovesicles.
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