Synthesis and Langmuir studies of bivalent and monovalent alpha-D-mannopyranosides with lectin Con A

"Surface Density of Ligands Controls In-Plane and Aggregative Modes of Multivalent Glycovesicle-Lectin Recognitions"

Glycovesicles are ideal tools to delineate finer mechanisms of the interactions at the biological cell membranes.  Multivalency forms the basis which, in turn, should surpass more than one mechanism in order to maintain multiple roles that the ligand-lectin interactions encounter.  Ligand densities hold a prime control to attenuate the interactions.  In the present study, mannose trisaccharide interacting with a cognate receptor, namely, Con A, is assessed at the vesicle surfaces.  A synthetic (1→3)(1→6)-branched mannose trisaccharide is tethered with a diacetylene monomer and glycovesicles of varying sugar densities are prepared.  The polydiacetylene vesicles are prepared by maintaining uniform lipid concentrations.  The interactions of the glycovesicles with the lectin are probed through dynamic light scattering and UV-Vis spectroscopy techniques.  Binding efficacies are assessed by surface plasmon resonance technique.  Aggregative and in-plane modes of interactions follow a ligand density-dependant manner at the vesicle surface. Vesicles with sparsely populated ligands engage lectin in an aggregative mode (trans-), leading to a cross-linked complex formation.  Whereas glycovesicles imbedded with dense ligands engage lectin interaction in an in-plane mode  intramolecularly (cis-).  Sub-nanomolar dissociation constants govern the intramolecular interaction occurring within the plane of the vesicle, relatively more efficacious than the aggregative intermolecular interactions.

Polyoxazolines with a Vicinally Double-Bioactivated Terminus for Biomacromolecular Affinity Assessment

Interactions between proteins and carbohydrates with larger biomacromolecules, e.g., lectins, are usually examined using self-assembled monolayers on target gold surfaces as a simplified model measuring setup. However, most of those measuring setups are either limited to a single substrate or do not allow for control over ligand distance and spacing. Here, we develop a synthetic strategy, consisting of a cascade of a thioesterification, native chemical ligation (NCL) and thiol-ene reaction, in order to create three-component polymer conjugates with a defined double bioactivation at the chain end. The target architecture is the vicinal attachment of two biomolecule residues to the α telechelic end point of a polymer and a thioether group at the ω chain end for fixating the conjugate to a gold sensor chip surface. As proof-of-principle studies for affinity measurements, we demonstrate the interaction between covalently bound mannose and ConA in surface acoustic wave (SAW) and surface plasmon resonance (SPR) experiments.

Multivalent glycoliposomes and micelles to study carbohydrate-protein and carbohydrate-carbohydrate interactions

This tutorial review describes multivalent carbohydrate-protein and carbohydrate-carbohydrate interaction studies that utilize self-assembled aggregates of thermodynamically stable liposomes and micelles. Strategies to prepare multivalent glycoliposomes and micelles include: (i) insertion of synthetic glycolipids into matrix lipids; (ii) preparation of glycolipids that aggregate to liposomes and micelles and (iii) modification of the hydrophilic surfaces with desired sugars. Several design strategies have been developed in order to obtain constituent glycolipids, having multivalent sugar moieties and their subsequent interactions with proteins were assessed in relation to the type of linkers that connect the hydrophilic and lipophilic segments. Lipophilic segments other than alkyl chains have also been developed. Polymer based glycoliposomes and micelles form an emphasis. Further, glycoliposomes facilitate studies of carbohydrate-carbohydrate interactions. An overview of the various types of glycoliposomes and micelles used to study carbohydrate-protein and carbohydrate-carbohydrate recognition phenomena is presented.

Mannose-decorated cyclodextrin vesicles: The interplay of multivalency and surface density in lectin-carbohydrate recognition

Cyclodextrin vesicles are versatile models for biological cell membranes since they provide a bilayer membrane that can easily be modified by host–guest interactions with functional guest molecules. In this article, we investigate the multivalent interaction of the lectin concanavalin A (ConA) with cyclodextrin vesicles decorated with mannose–adamantane conjugates with one, two or three adamantane units as well as one or two mannose units. The carbohydrate–lectin interaction in this artificial, self-assembled glycocalyx was monitored in an agglutination assay by the increase of optical density at 400 nm. It was found that there is a close relation between the carbohydrate density at the cyclodextrin vesicle surface and the multivalent interaction with ConA, and the most efficient interaction (i.e., fastest agglutination at lowest concentration) was observed for mannose–adamantane conjugates, in which both the cyclodextrin–adamantane and the lectin–mannose interaction is inherently multivalent.

Multivalent interaction of cyclodextrin vesicles, carbohydrate guests, and lectins: a kinetic investigation

An artificial glycocalix self-assembles when unilamellar bilayer vesicles of amphiphilic β-cyclodextrins are decorated with maltose- and lactose-adamantane conjugates by host-guest interactions. The maltose-decorated vesicles aggregate in the presence of lectin concanavalin A whereas the lactose-decorated vesicles aggregate in the presence of lectin peanut agglutinin. The kinetics of the orthogonal multivalent interfacial interactions present in this ternary system of vesicles, carbohydrates, and lectins were studied by time-dependent measurements of the optical density at 400 nm. The average vesicle and vesicle aggregate sizes were monitored by dynamic light scattering. The aggregation process was evaluated as a function of lectin concentration, vesicle concentration, and surface coverage of the vesicles by the carbohydrate-adamantane conjugates. The initial rate of vesicle aggregation scales linearly with the lectin as well as the cyclodextrin vesicle concentration. Furthermore, each lectin requires a characteristic critical density of carbohydrates at the vesicle surface. These observations allow a prediction of the response of the ternary supramolecular system at different concentrations of its components. Also, the effective binding site separation in a multivalent receptor such as a multiple binding site protein can be accurately determined. This methodology can be extended to multivalent noncovalent interactions in other ligand-receptor systems at interfaces.

Two-dimensional supramolecular assemblies involving neoglycoplipids: Self-organization and insertion properties into Langmuir monolayers

In nature, interfacial molecular recognition and chirality are of fundamental significance for the construction of biological assemblies. Lipid monolayers at liquid interface can be used as biomimetic models for studying molecular interactions in such assemblies. In this article, we will focus on the use of Langmuir monolayers for studying self-organization and insertion properties of several neoglycolipids. Two types of glycolipids have been considered, one in the context of the analysis of glycoconjugates of biological relevance, and one dealing with the ability of some glycoprobes to insert into a monolayer in relation with their efficiency for serving as membrane imaging systems.

Novel photoinduced grafting-chemical reaction sequence for the construction of a glycosylation surface

Carbohydrates play a major role in many recognition events, such as blood coagulation, immune response, fertilization, cell growth, embryogenesis, and cellular signal transfer, which are essential for the survival of living entities. Synthetic carbohydrate-based polymers, so-called glycopolymers, are emerging as important well-defined tools for investigating carbohydrate-based biological processes and for simulating various functions of carbohydrates. In this work, we present a facile strategy for the formation of glycopolymer tethered on polypropylene microporous membrane surface. Acrylamide was grafted onto the polypropylene microporous membrane surface by photoinduced graft polymerization in the presence of benzophenone. The amide groups of grafted poly(acrylamide) were then transformed to primary amine groups by the Hofmann rearrangement reaction. Quantificational evaluation of the rearrangement reaction was carried out by ninhydrin method and mass weighting. Sugar moieties were coupled with the grafted functional layer to form glycopolymer by the reaction between primary amine groups and carbohydrate lactones. The grafting of acrylamide, the conversion of amide groups to amine groups, and the coupling of sugar moieties were confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy combined with surface morphology observation by scanning electron microscopy.

Fabrication of glycosylated surface on polymer membrane by UV-induced graft polymerization for lectin recognition

Increasingly, carbohydrate-protein interactions are viewed as important mechanisms for many biological processes such as blood coagulation, immune response, viral infection, inflammation, embryogenesis, and cellular signal transfer. However, the weak affinity of the interactions and the structural complexity of carbohydrates have hindered efforts to develop a comprehensive understanding of carbohydrate functions. Fortunately, synthetic polyvalent glycoligands give us a chance to reveal the nature of these biological processes. In this work a sugar-containing monomer (alpha-D-allyl glucoside (AG)) was grafted onto polypropylene microporous membrane (PPMM) by UV-induced graft polymerization to generate a glycosylated porous surface for the first time. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy were employed to confirm the glycosylation. Water contact angle measurement was used to evaluate the hydrophilicity change of the surfaces before and after the graft polymerization of AG. It was found that the grafting density increased reasonably with the increase of AG monomer concentration, and then this increase slowed when the AG concentration exceeded 80 g/L. At the same time a 20-25 min UV irradiation was enough for the grafting polymerization. The photoinitiator concentration also influenced the grafting density obviously, and there was an optimal concentration of the photoinitiator for the grafting process. The water contact angle of the polyAG-tethered membrane surface decreased from 149 degrees to 80 degrees with the increase of grafting density from 0 to 187.76 microg/cm2, which indicated a hydrophilic variation of the membrane surface by the grafting of AG. Results also indicated that the surface-grafted polyAG chains showed weak interaction with Con A when the grafting density was low. However, when the sugar density exceeded 90 microg/cm2, the binding affinity increased dramatically which was the due to the "glycoside cluster effect".

Evaluation of α-d-mannopyranoside glycolipid micelles–lectin interactions by surface plasmon resonance method

It is established that achieving higher binding affinities in carbohydrate-protein interactions requires multivalent presentations of the sugar ligands at the receptor binding site. Several inhibition, calorimetric, mass balance, and other studies have reiterated the beneficial effects of molecular level clustering of the sugar ligands for tight binding to the receptors. We have undertaken an effort to study the multivalent effects involving larger assemblies, represented by micelles, and their lectin interactions. The micelles were constituted with monomer bearing one- or two-sugar moieties at the monomolecular level and with varying the distances between the sugar moieties. Micellar aggregation studies and dynamic light scattering (DLS) studies afforded details of the aggregation numbers and the hydrodynamic diameters of various glycolipid (GL) micelles. The GL micelles were used as analytes of surface plasmon resonance (SPR) experiments on a lectin concanavalin A (Con A)-immobilized surface. SPR studies of the micelle-lectin interactions demonstrate that the ligand-receptor binding can be fit into the bivalent analyte model of interaction. Furthermore, micelles formed from two-sugar containing GLs are able to elicit favorable kinetic association rate constants in comparison to the micelles constituted with one-sugar containing GLs. The kinetic rate constants across the micelles and the effect of the sugar valencies in the GLs are discussed.