Triggerable Multivalent Glyconanoparticles for Probing Carbohydrate-Carbohydrate Interactions

Recent Advances in Polymers Bearing Activated Esters for the Synthesis of Glycopolymers by Postpolymerization Modification

Glycopolymers are functional polymers with saccharide moieties on their side chains and are attractive candidates for biomaterials. Postpolymerization modification can be employed for the synthesis of glycopolymers. Activated esters are useful in various fields, including polymer chemistry and biochemistry, because of their high reactivity and ease of reaction. In particular, the formation of amide bonds caused by the reaction of activated esters with amino groups is of high synthetic chemical value owing to its high selectivity. It has been employed in the synthesis of various functional polymers, including glycopolymers. This paper reviews the recent advances in polymers bearing activated esters for the synthesis of glycopolymers by postpolymerization modification. The development of polymers bearing hydrophobic and hydrophilic activated esters is described. Although water-soluble activated esters are generally unstable and hydrolyzed in water, novel polymer backbones bearing water-soluble activated esters are stable and useful for postpolymerization modification for synthesizing glycopolymers in water. Dual postpolymerization modification can be employed to modify polymer side chains using two different molecules. Thiolactone and glycine propargyl esters on the polymer backbone are described as activated esters for dual postpolymerization modification.

Sweet Janus Particles: Multifunctional Inhibitors of Carbohydrate-Based Bacterial Adhesion

Escherichia coli and other bacteria use adhesion receptors, such as FimH, to attach to carbohydrates on the cell surface as the first step of colonization and infection. Efficient inhibitors that block these interactions for infection treatment are multivalent carbohydrate-functionalized scaffolds. However, these multivalent systems often lead to the formation of large clusters of bacteria, which may pose problems for clearing bacteria from the infected site. Here, we present Man-containing Janus particles (JPs) decorated on one side with glycomacromolecules to target Man-specific adhesion receptors of E. coli. On the other side, poly(N-isopropylacrylamide) is attached to the particle hemisphere, providing temperature-dependent sterical shielding against binding and cluster formation. While homogeneously functionalized particles cluster with multiple bacteria to form large aggregates, glycofunctionalized JPs are able to form aggregates only with individual bacteria. The formation of large aggregates from the JP-decorated single bacteria can still be induced in a second step by increasing the temperature and making use of the collapse of the PNIPAM hemisphere. This is the first time that carbohydrate-functionalized JPs have been derived and used as inhibitors of bacterial adhesion. Furthermore, the developed JPs offer well-controlled single bacterial inhibition in combination with cluster formation upon an external stimulus, which is not achievable with conventional carbohydrate-functionalized particles.

Development of a cell-based quaternary system to unveil the effect of pectic polysaccharides on oral astringency

Phenolic compounds are responsible for food unpleasant taste properties, including astringency, due to their ability to interact with salivary proteins and oral constituents. Astringency is a crucial attribute for consumer's acceptability. To fulfill the demand for both healthy and tasty food, polysaccharides raise as a good alternative to modulate astringency. In this work, a cell-based quaternary system was developed to evaluate the ability of polysaccharides to reduce the interaction between two classes of hydrolysable tannins - gallotannins (tannic acid) and ellagitannins (punicalagin) - and oral constituents (cells, salivary proteins and mucosal pellicle). So, pectic polysaccharide fractions isolated from grape skins, imidazole soluble polysaccharides (ISP) and carbonate soluble polysaccharides (CSP), as well as a commercial pectin, were tested. Results showed that the polysaccharide's effect depends on the structural features of the molecules involved. CSP fraction and pectin were the most effective, reducing the interactions between both tannins and the oral constituents, mainly in the complete oral model. The highest uronic acid content and the presence of methyl esterified groups could explain their high reduction ability. For tannic acid, the reduction effect increased along with the galloylation degree, while the interaction of β-punicalagin with the oral constituents was practically inhibited at 3.0 mg.mL-1.

Specific Binding of Ligand-Functionalized Thermoresponsive Microgels: Effect of Architecture, Ligand Density, and Hydrophobicity

The biomolecular interaction of ligand-presenting switchable microgels is studied with respect to the polymer type, composition, and structure of the microgels. Monodisperse microgels are prepared through precipitation polymerization of N-isopropylacrylamide (PNIPAM microgels) or oligo(ethylene glycol methacrylamide)s (POEGMA microgels) in the presence of crosslinkers or in their absence (self-crosslinked). Functionalization with mannose or biotin as model ligands and affinity measurements upon heating/cooling are conducted to obtain mechanistic insights into how the microgel phase transition affects the specific interactions. In particular, we are interested in adjusting the crosslinking, swelling degree, and ligand density of mannose-functionalized microgels to reversibly catch and release mannose binding Escherichia coli by setting the temperature below or above the microgels' volume phase transition temperature (VPTT). The increased mannose density for collapsed microgels above the VPTT results in stronger E. coli binding. Detachment of E. coli by reswelling the microgels below the VPTT is achieved only for self-crosslinked microgels showing a stronger decrease in ligand density compared to microgels with dedicated crosslinkers. Owing to a reduced mannose density in the shell of POEGMA microgels, their E. coli binding was lower compared to PNIPAM microgels, as supported by ultraresolution microscopy. Importantly, an inverse temperature-controlled binding of microgels decorated with hydrophilic mannose and hydrophobic biotin ligands is observed. This indicates that hydrophobic ligands are inaccessible in the collapsed hydrophobic network above the VPTT, whereas hydrophilic mannose units are then enriched at the microgel-water interface and thus are more accessible.

Upper Critical Solution Temperature Polyvalent Scaffolds Aggregate and Exterminate Bacteria

Specific recognition and strong affinities of bacteria receptors with the host cell glycoconjugates pave the way to control the bacteria aggregation and kill bacteria. Herein, using aggregation-induced emission (AIE) molecules decorated upper critical solution temperature (UCST) polyvalent scaffold (PATC-GlcN), an approach toward visualizing bacteria aggregation and controlling bacteria-polyvalent scaffolds affinities under temperature stimulus is described. Polyvalent scaffolds with diblocks, one UCST block PATC of polyacrylamides showing a sharp UCST transition and typical AIE behavior, the second bacteria recognition block GlcN of hydrophilic glucosamine modified polyacrylamide, are prepared through a reversible addition and fragmentation chain transfer polymerization. Aggregated chain conformation of polyvalent scaffolds at temperature below UCST induces the aggregation of E. coli ATCC8739, because of the high density of glucosamine moieties, whereas beyond UCST, the hydrophilic state of the scaffolds dissociates the bacteria aggregation. The sweet-talking of bacteria toward the polyvalent scaffolds can be visualized by the fluorescent imaging technique, simultaneously. Due to the specific recognition of polyvalent scaffolds with bacteria, the photothermal agent IR780 loaded PATC-GlcN shows the targeted killing ability toward E. coli ATCC8739 in vitro and in vivo under NIR radiation.

Temperature-Controlled Adhesion to Carbohydrate Functionalized Microgel Films: An E. coli and Lectin Binding Study

The preparation of thermoresponsive mannose functionalized monolayers of poly(N-isopropylacrylamide) microgels and the analysis of the specific binding of concanavalin A (ConA) and E. coli above and below the lower critical solution temperature (LCST) are shown. Via inhibition and direct binding assays it is found that ConA binding is time-dependent, where at short incubation times binding is stronger above the LCST. Given larger incubation times, the interaction of ConA to the microgel network is increased below the LCST when compared to temperatures above the LCST, possibly due to increased ConA diffusion and multivalent binding in the more open microgel network below the LCST. For E. coli, which presents only monovalent lectins and is too large to diffuse into the network, binding is always enhanced above the LCST. This is due to the larger mannose density of the microgel layer above the LCST increasing the interaction to E. coli. Once bound to the microgel layer above the LCST, E. coli cannot be released by cooling down below the LCST. Overall, this suggests that the carbohydrate presenting microgel layers enable specific binding where the temperature-induced transition between swollen and collapsed microgels may increase or decrease binding depending on the receptor size.

Lectin and E. coli Binding to Carbohydrate-Functionalized Oligo(ethylene glycol)-Based Microgels: Effect of Elastic Modulus, Crosslinker and Carbohydrate Density

The synthesis of carbohydrate-functionalized biocompatible poly(oligo(ethylene glycol) methacrylate microgels and the analysis of the specific binding to concanavalin A (ConA) and Escherichia coli (E. coli) is shown. By using different crosslinkers, the microgels' size, density and elastic modulus were varied. Given similar mannose (Man) functionalization degrees, the softer microgels show increased ConA uptake, possibly due to increased ConA diffusion in the less dense microgel network. Furthermore, although the microgels did not form clusters with E. coli in solution, surfaces coated with mannose-functionalized microgels are shown to bind the bacteria whereas galactose (Gal) and unfunctionalized microgels show no binding. While ConA binding depends on the overall microgels' density and Man functionalization degree, E. coli binding to microgels' surfaces appears to be largely unresponsive to changes of these parameters, indicating a rather promiscuous surface recognition and sufficiently strong anchoring to few surface-exposed Man units. Overall, these results indicate that carbohydrate-functionalized biocompatible oligo(ethylene glycol)-based microgels are able to immobilize carbohydrate binding pathogens specifically and that the binding of free lectins can be controlled by the network density.

Switchable Adhesion of E. coli to Thermosensitive Carbohydrate-Presenting Microgel Layers: A Single-Cell Force Spectroscopy Study

Adhesion processes at the cellular scale are dominated by carbohydrate interactions, including the attachment and invasion of pathogens. Carbohydrate-presenting responsive polymers can bind pathogens and inhibit pathogen invasion by remote stimuli for the development of new antibiotic strategies. In this work, the adhesion forces of E. coli to monolayers composed of mannose-functionalized microgels with thermosensitive poly(N-isopropylacrylamide) (PNIPAM) and poly(oligo(ethylene glycol)) (PEG) networks are quantified using single-cell force spectroscopy (SCFS). When exceeding the microgels' lower critical solution temperature (LCST), the adhesion increases up to 2.5-fold depending on the polymer backbone and the mannose density. For similar mannose densities, the softer PNIPAM microgels show a significantly stronger adhesion increase when crossing the LCST as compared to the stiffer PEG microgels. This is explained by a stronger shift in swelling, mannose density, and surface roughness of the softer gels when crossing the LCST. When using nonbinding galactose instead of mannose, or when inhibiting bacterial receptors, a certain level of adhesion remains, indicating that also polymer-fimbria entanglements contribute to adhesion. The presented quantitative analysis provides insights into carbohydrate-mediated bacterial adhesion and the relation to material properties and shows the prospects and limitations of interactive polymer materials to control the attachment of bacteria.

The influence of ABO blood groups on COVID-19 susceptibility and severity: A molecular hypothesis based on carbohydrate-carbohydrate interactions

The world is experiencing one of the most difficult moments in history with the COVID-19 pandemic, a disease caused by SARS-CoV-2, a new type of coronavirus. Virus infectivity is mediated by the binding of Spike transmembrane glycoprotein to specific protein receptors present on cell host surface. Spike is a homotrimer that emerges from the virion, each monomer containing two subunits named S1 and S2, which are related to cell recognition and membrane fusion, respectively. S1 is subdivided in domains S1A (or NTD) and S1B (or RBD), with experimental and in silico studies suggesting that the former binds to sialic acid-containing glycoproteins, such as CD147, whereas the latter binds to ACE2 receptor. Recent findings indicate that the ABO blood system modulates susceptibility and progression of infection, with type-A individuals being more susceptible to infection and/or manifestation of a severe condition. Seeking to understand the molecular mechanisms underlying this susceptibility, we carried out an extensive bibliographic survey on the subject. Based on this survey, we hypothesize that the correlation between the ABO blood system and susceptibility to SARS-CoV-2 infection can be presumably explained by the modulation of sialic acid-containing receptors distribution on host cell surface induced by ABO antigens through carbohydrate-carbohydrate interactions, which could maximize or minimize the virus Spike protein binding to the host cell. This model could explain previous sparse observations on the molecular mechanism of infection and can direct future research to better understand of COVID-19 pathophysiology.

Glycan Nanobiosensors

This review paper comprehensively summarizes advances made in the design of glycan nanobiosensors using diverse forms of nanomaterials. In particular, the paper covers the application of gold nanoparticles, quantum dots, magnetic nanoparticles, carbon nanoparticles, hybrid types of nanoparticles, proteins as nanoscaffolds and various nanoscale-based approaches to designing such nanoscale probes. The article covers innovative immobilization strategies for the conjugation of glycans on nanoparticles. Summaries of the detection schemes applied, the analytes detected and the key operational characteristics of such nanobiosensors are provided in the form of tables for each particular type of nanomaterial.

"Tuning aggregative versus non-aggregative lectin binding with glycosylated nanoparticles by the nature of the polymer ligand"

Glycan-lectin interactions drive a diverse range of biological signaling and recognition processes. The display of glycans in multivalent format enables their intrinsically weak binding affinity to lectins to be overcome by the cluster glycoside effect, which results in a non-linear increase in binding affinity. As many lectins have multiple binding sites, upon interaction with glycosylated nanomaterials either aggregation or surface binding without aggregation can occur. Depending on the application area, either one of these responses are desirable (or undesirable) but methods to tune the aggregation state, independently from the overall extent/affinity of binding are currently missing. Herein, we use gold nanoparticles decorated with galactose-terminated polymer ligands, obtained by photo-initiated RAFT polymerization to ensure high end-group fidelity, to show the dramatic impact on agglutination behaviour due to the chemistry of the polymer linker. Poly(N-hydroxyethyl acrylamide) (PHEA)-coated gold nanoparticles, a polymer widely used as a non-ionic stabilizer, showed preference for aggregation with lectins compared to poly(N-(2-hydroxypropyl)methacrylamide) (PHPMA)-coated nanoparticles which retained colloidal stability, across a wide range of polymer lengths and particle core sizes. Using biolayer interferometry, it was observed that both coatings gave rise to similar binding affinity and hence provided conclusive evidence that aggregation rate alone cannot be used to measure affinity between nanoparticle systems with different stabilizing linkers. This is significant, as turbidimetry is widely used to demonstrate glycomaterial activity, although this work shows the most aggregating may not be the most avid, when comparing different polymer backbones/coating. Overall, our findings underline the potential of PHPMA as the coating of choice for applications where aggregation upon lectin binding would be problematic, such as in vivo imaging or drug delivery.

Self-assembly of bacteria cellulose hydrogels carrying multiple carbohydrate appendages to visualize carbohydrate-carbohydrate interactions

Nata de coco was chemically modified to afford the bacterial cellulose hydrogels carrying terminal alkynes. The resultant hydrogels were then converted into hydrogels carrying lactosides or those carrying α-2,3-sialyllactosides by the Cu⁺-catalyzed alkyne-azide cyclization. The stable homo association of the hydrogels carrying lactosides was observed in an aqueous solution containing Ca²⁺, thereby demonstrating the Ca²⁺-mediated lactoside-lactoside interactions. Ca²⁺ also stabilized the hetero associations among the hydrogels carrying lactosides and those carrying α-2,3-sialyllactosides, thereby also demonstrating the Ca²⁺-induced interactions between the lactosides and the α-2,3-sialyllactosides. The sizes of these hydrogels were of the order of ca. 5 mm, and their associations could thus be readily monitored with the naked eye.

Thermosensitive Display of Carbohydrate Ligands on Microgels for Switchable Binding of Proteins and Bacteria

The synthesis of carbohydrate-functionalized thermosensitive poly(N-isopropylacrylamide) microgels and their ability to bind carbohydrate-binding pathogens upon temperature switch are reported. It is found that the microgels' binding affinity is increased above their lower critical solution temperature (LCST), enabling thermo-triggerable capture of pathogens. Here, a series of microgels with comparatively low mannose functionalization degrees below 1 mol % is achieved by a single polymerization step. Upon increase in mannose density, the microgel size increases, and the LCST decreases to 26 °C. Clustering with concanavalin A indicated that binding affinity is enhanced by a higher mannose content and by raising the temperature above the LCST. Binding studies with Escherichia coli confirm stronger specific interactions above the LCST and formation of mechanically stable aggregates enabling efficient separation of E. coli by filtration. For small incubation times above the LCST, the microgels' potential to release pathogens again below the LCST is confirmed also. Compared to existing switchable scaffolds, microgels nearly entirely composed of a thermosensitive material undergo a large change in volume, which allows them to drastically vary the density of ligands to switch between capture and release. This straightforward yet novel approach is likely compatible with a broad range of bioactive ligands. Therefore, thermosensitive microgels represent a promising platform for the specific capture or release of cells or pathogens.

The glyconanoparticle as carrier for drug delivery

The glyconanoparticle (GlycoNP) has multiple effects and has important applications in drug delivery and bioimaging. It not only has the advantages of nano drug delivery system but also utilizes the characteristics of multivalent interaction of sugar, which greatly improves the targeting of drug delivery. Herein, the application of GlycoNP in drug delivery was analyzed and discussed, the solution to its problem was proposed, and its prospects were forecasted.

Synthesis of Sub-100 nm Glycosylated Nanoparticles via a One Step, Free Radical, and Surfactant Free Emulsion Polymerization

The facile synthesis of sub-100 nm glyco nanoparticles is presented via a one-step, free radical, and surfactant free emulsion polymerization. It is shown that by using sterically large, hydrophilic glycomonomers such as a lactose acrylamide with the charged azo initiator 4,4'-azobis(4-cyanovaleric acid), growing particles are stabilized enough to reproducibly produce well defined (PDi ≤ 0.1) glycoparticles with diameters below 100 nm.