Effects of the Surface Densities of Glycoclusters on the Determination of Their IC50andKdValue Determination by Using a Microarray

CDs-Peroxyfluor Conjugation for Ratiometric Fluorescence Detection of Glucose and Shortening Its Detection Time from Reaction Dynamic Perspective

A ratiometric fluorescence probe based on the conjugation of peroxyfluor-NHS (PF) and carbon dots (CDs) was designed for selective and rapid detection of glucose. When glucose was catalytically oxidized by glucose oxidase (GOx), the product H₂O₂ would react with colorless and non-fluorescent peroxyfluor moiety to give the colored and fluorescent fluorescein moiety which would absorb the energy of CDs emission at 450 nm due to the Förster Resonance Energy Transfer (FRET) and generate a new emission peak at 517 nm. The reaction between PF and H₂O₂ was slow with a rate constant of about 2.7 × 10^-4 s^-1 under pseudo-first-order conditions (1 uM PF, 1 mM H₂O₂), which was unconducive to rapid detection. Given this, a short time detection method was proposed by studying the kinetics of the reaction between PF and H₂O₂. In this method, the detection time was fixed at three minutes. The linear detection of glucose could be well realized even if the reaction was partially done. As glucose concentration increased from 0.05 mM to 5 mM, the fluorescence intensity ratio (I₅₁₇/I₄₅₀) after 3 minutes' reaction of CDs-PF and glucose oxidation products changed linearly from 0.269 to 1.127 with the limit of detection (LOD) of 17.19 μM. In addition, the applicability of the probe in blood glucose detection was verified.

Flexible Label-Free Platinum and Bio-PET-Based Immunosensor for the Detection of SARS-CoV-2

The demand for new devices that enable the detection of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) at a relatively low cost and that are fast and feasible to be used as point-of-care is required overtime on a large scale. In this sense, the use of sustainable materials, for example, the bio-based poly (ethylene terephthalate) (Bio-PET) can be an alternative to current standard diagnostics. In this work, we present a flexible disposable printed electrode based on a platinum thin film on Bio-PET as a substrate for the development of a sensor and immunosensor for the monitoring of COVID-19 biomarkers, by the detection of L-cysteine and the SARS-CoV-2 spike protein, respectively. The electrode was applied in conjunction with 3D printing technology to generate a portable and easy-to-analyze device with a low sample volume. For the L-cysteine determination, chronoamperometry was used, which achieved two linear dynamic ranges (LDR) of 3.98-39.0 μmol L^-1 and 39.0-145 μmol L^-1, and a limit of detection (LOD) of 0.70 μmol L^-1. The detection of the SARS-CoV-2 spike protein was achieved by both square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) by a label-free immunosensor, using potassium ferro-ferricyanide solution as the electrochemical probe. An LDR of 0.70-7.0 and 1.0-30 pmol L^-1, with an LOD of 0.70 and 1.0 pmol L^-1 were obtained by SWV and EIS, respectively. As a proof of concept, the immunosensor was successfully applied for the detection of the SARS-CoV-2 spike protein in enriched synthetic saliva samples, which demonstrates the potential of using the proposed sensor as an alternative platform for the diagnosis of COVID-19 in the future.

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.

Deciphering multivalent glycocluster-lectin interactions through AFM characterization of the self-assembled nanostructures

Pseudomonas aeruginosa is a human opportunistic pathogen responsible for lung infections in cystic fibrosis patients. The emergence of resistant strains and its ability to form a biofilm seem to give a selective advantage to the bacterium and thus new therapeutic approaches are needed. To infect the lung, the bacterium uses several virulence factors, like LecA lectins. These proteins are involved in bacterial adhesion due to their specific interaction with carbohydrates of the host epithelial cells. The tetrameric LecA lectin specifically binds galactose residues. A new therapeutic approach is based on the development of highly affine synthetic glycoclusters able to selectively link with LecA to interfere with the natural carbohydrate-LecA interaction. In this study, we combined atomic force microscopy imaging and molecular dynamics simulations to visualize and understand the arrangements formed by LecA and five different glycoclusters. Our glycoclusters are small scaffolds characterized by a core and four branches, which terminate in a galactose residue. Depending on the nature of the core and the branches, the glycocluster-lectin interaction can be modulated and the affinity increased. We show that glycocluster-LecA arrangements highly depend on the glycocluster architecture: the core influences the rigidity of the geometry and the directionality of the branches, whereas the nature of the branch determines the compactness of the structure and the ease of binding.

Screening of a Library of Oligosaccharides Targeting Lectin LecB of Pseudomonas Aeruginosa and Synthesis of High Affinity Oligoglycoclusters

The Gram negative bacterium Pseudomonas aeruginosa (PA) is an opportunistic bacterium that causes severe and chronic infection of immune-depressed patients. It has the ability to form a biofilm that gives a selective advantage to the bacteria with respect to antibiotherapy and host defenses. Herein, we have focused on the tetrameric soluble lectin which is involved in bacterium adherence to host cells, biofilm formation, and cytotoxicity. It binds to l-fucose, d-mannose and glycan exposing terminal fucose or mannose. Using a competitive assay on microarray, 156 oligosaccharides and polysaccharides issued from fermentation or from the biomass were screened toward their affinity to LecB. Next, the five best ligands (Lewis^a, Lewis^b, Lewis^x, siayl-Lewis^x and 3-fucosyllactose) were derivatized with a propargyl aglycon allowing the synthesis of 25 trivalent, 25 tetravalent and 5 monovalent constructions thanks to copper catalyzed azide alkyne cycloaddition. The 55 clusters were immobilized by DNA Directed immobilization leading to the fabrication of a glycocluster microarray. Their binding to LecB was studied. Multivalency improved the binding to LecB. The binding structure relationship of the clusters is mainly influenced by the carbohydrate residues. Molecular simulations indicated that the simultaneous contact of both binding sites of monomer A and D seems to be energetically possible.

Identification of Nanomolar Lectin Ligands by a Glycodendrimer Microarray

Carbohydrate-protein interactions play key roles in a wide variety of biological processes. These interactions are usually weak, with dissociation constants in the low millimolar to high micromolar range. Nature uses multivalency to reach high avidities via the glycoside cluster effect. Capitalizing on this effect, numerous synthetic multivalent glycoconjugates have been described and used as ligands for carbohydrate-binding proteins. However, valency is only one of the several parameters governing the binding mechanisms that are different for every biological receptor, making it almost impossible to predict. In this context, ligand optimization requires the screening of a large number of structures with different valencies, rigidities/flexibilities, and architectures. In this article, we describe a screening platform based on a glycodendrimer array and its use to determine the key parameters for high-affinity ligands of lectin. Several glycoclusters and glycodendrimers displaying varying numbers of α-N-acetylgalactosamine residues were covalently attached on glass slides, and their bindings were studied with the fluorophore-functionalized Helix pomatia agglutinin (HPA) used as a lectin model. This technique requires minimal quantities of glycoconjugate compared to those for other techniques and affords useful information on the binding strength. Building of the glycodendrimer array and quantification of the interactions with HPA are described.

Therapeutic Antibodies to Ganglioside GD2 Evolved from Highly Selective Germline Antibodies

Antibodies play a crucial role in host defense and are indispensable research tools, diagnostics, and therapeutics. Antibody generation involves binding of genomically encoded germline antibodies followed by somatic hypermutation and in vivo selection to obtain antibodies with high affinity and selectivity. Understanding this process is critical for developing monoclonal antibodies, designing effective vaccines, and understanding autoantibody formation. Prior studies have found that antibodies to haptens, peptides, and proteins evolve from polyspecific germline antibodies. The immunological evolution of antibodies to mammalian glycans has not been studied. Using glycan microarrays, protein microarrays, cell binding studies, and molecular modeling, we demonstrate that therapeutic antibodies to the tumor-associated ganglioside GD2 evolved from highly specific germline precursors. The results have important implications for developing vaccines and monoclonal antibodies that target carbohydrate antigens. In addition, they demonstrate an alternative pathway for antibody evolution within the immune system that is distinct from the polyspecific germline pathway.

Intervention effects of five cations and their correction on hemolytic activity of tentacle extract from the jellyfish Cyanea capillata

Cations have generally been reported to prevent jellyfish venom-induced hemolysis through multiple mechanisms by spectrophotometry. Little attention has been paid to the potential interaction between cations and hemoglobin, potentially influencing the antagonistic effect of cations. Here, we explored the effects of five reported cations, La³⁺, Mn²⁺, Zn²⁺, Cu²⁺ and Fe²⁺, on a hemolytic test system and the absorbance of hemoglobin, which was further used to measure their effects on the hemolysis of tentacle extract (TE) from the jellyfish Cyanea capillata. All the cations displayed significant dose-dependent inhibitory effects on TE-induced hemolysis with various dissociation equilibrium constant (K_d) values as follows: La³⁺ 1.5 mM, Mn²⁺ 93.2 mM, Zn²⁺ 38.6 mM, Cu²⁺ 71.9 μM and Fe²⁺ 32.8 mM. The transparent non-selective pore blocker La³⁺ did not affect the absorbance of hemoglobin, while Mn²⁺ reduced it slightly. Other cations, including Zn²⁺, Cu²⁺ and Fe²⁺, greatly decreased the absorbance with K_d values of 35.9, 77.5 and 17.6 mM, respectively. After correction, the inhibitory K_d values were 1.4 mM, 45.8 mM, 128.5 μM and 53.1 mM for La³⁺, Zn²⁺, Cu²⁺ and Fe²⁺, respectively. Mn²⁺ did not inhibit TE-induced hemolysis. Moreover, the inhibitory extent at the maximal given dose of all cations except La³⁺ was also diminished. These corrected results from spectrophotometry were further confirmed by direct erythrocyte counting under microscopy. Our results indicate that the cations, except for La³⁺, can interfere with the absorbance of hemoglobin, which should be corrected when their inhibitory effects on hemolysis by jellyfish venoms are examined. The variation in the inhibitory effects of cations suggests that the hemolysis by jellyfish venom is mainly attributed to the formation of non-selective cation pore complexes over other potential mechanisms, such as phospholipases A2 (PLA2), polypeptides, protease and oxidation. Blocking the pore-forming complexes may be a primary strategy to improve the in vivo damage and mortality from jellyfish stings due to hemolytic toxicity.

Toward the Rational Design of Galactosylated Glycoclusters That Target Pseudomonas aeruginosa Lectin A (LecA): Influence of Linker Arms That Lead to Low-Nanomolar Multivalent Ligands

Anti-infectious strategies against pathogen infections can be achieved through antiadhesive strategies by using multivalent ligands of bacterial virulence factors. LecA and LecB are lectins of Pseudomonas aeruginosa implicated in biofilm formation. A series of 27 LecA-targeting glycoclusters have been synthesized. Nine aromatic galactose aglycons were investigated with three different linker arms that connect the central mannopyranoside core. A low-nanomolar (Kd =19 nm, microarray) ligand with a tyrosine-based linker arm could be identified in a structure-activity relationship study. Molecular modeling of the glycoclusters bound to the lectin tetramer was also used to rationalize the binding properties observed.