Probing multivalency in ligand–receptor-mediated adhesion of soft, biomimetic interfaces

Abstract

SummaryMany biological functions at cell level are mediated by the glycocalyx, a dense carbohydrate-presenting layer. In this layer specific interactions between carbohydrate ligands and protein receptors are formed to control cell–cell recognition, cell adhesion and related processes. The aim of this work is to shed light on the principles of complex formation between surface anchored carbohydrates and receptor surfaces by measuring the specific adhesion between surface bound mannose on a concanavalin A (ConA) layer via poly(ethylene glycol)-(PEG)-based soft colloidal probes (SCPs). Special emphasis is on the dependence of multivalent presentation and density of carbohydrate units on specific adhesion. Consequently, we first present a synthetic strategy that allows for controlled density variation of functional groups on the PEG scaffold using unsaturated carboxylic acids (crotonic acid, acrylic acid, methacrylic acid) as grafting units for mannose conjugation. We showed by a range of analytic techniques (ATR–FTIR, Raman microscopy, zeta potential and titration) that this synthetic strategy allows for straightforward variation in grafting density and grafting length enabling the controlled presentation of mannose units on the PEG network. Finally we determined the specific adhesion of PEG-network-conjugated mannose units on ConA surfaces as a function of density and grafting type. Remarkably, the results indicated the absence of a molecular-level enhancement of mannose/ConA interaction due to chelate- or subsite-binding. The results seem to support the fact that weak carbohydrate interactions at mechanically flexible interfaces hardly undergo multivalent binding but are simply mediated by the high number of ligand–receptor interactions.

Elastic Modulus Dependence on the Specific Adhesion of Hydrogels

“…The mixture was stirred overnight at room temperature under a hydrogen atmosphere. [23] Briefly, water was exchanged by ethanol, and benzophenone (250 mg, 1.4 mmol) and crotonic acid (1.5 g, 17.4 mmol) were added. The filtrate was concentrated removing the organic solvents and the resulting solution was washed with chloroform (3 × 50.0 mL).…”

“…CA adds to the radicals at growing PEG-dAAm chains and essentially caps the crosslinking sites, as it is known to not homopolymerize under the applied conditions. [23,24] As a result, we obtained PEG-CA SCPs with a CA functionalization degree on the order of 120 µmol g −1 (dried particles) as measured via toluidine blue titration (Section S3, Supporting Information). The elastic moduli of the final SCPs were determined by AFM force-indentation measurements (Section S1, Supporting Information).…”

Multivalent Interactions of Polyamide Based Sequence‐Controlled Glycomacromolecules with Concanavalin A

“…Given the low affinity of protein–carbohydrate interactions, it is important to design multivalent carbohydrates exhibiting biologically relevant interaction to protein receptors. Researchers have established various types of scaffolds presenting sugars for high‐affinity binding, for example, 2D surfaces, microgels, nanoparticles, hydrogel beads, dendrimers, or polymers . Due to the low affinity and comparatively short lifetime of single carbohydrate–protein complexes, carbohydrates presented on polymeric scaffolds (glycopolymers) predominantly show an additive, “statistical” contribution when binding to receptors .…”

Hydrogel Microparticles as Sensors for Specific Adhesion: Case Studies on Antibody Detection and Soil Release Polymers

“…For the two adhesion assays, antibody detection and soil release polymer characterization, two types of SCPs were prepared: antigen and cellobiose functionalized SCPs. In order to introduce coupling groups for the antigen and cellobiose for the adhesion assay, crotonic acid (CA) was grafted in the PEG-dAAm network under UV irradiation using benzophenone as active photophore [21,22]. Accordingly, PEG-CA SCPs with a CA functionalization degree on the order of 120 µmol CA per 1 g PEG-CA were obtained as measured via Toluidine blue O (TBO) titration.…”

“…The resulting particles were 10-70 µm in diameter. Next, the PEG SCPs were grafted with crotonic acid (CA) [21]. Briefly …”