Screening of a Glycopolymer Library of GM1 Mimics Containing Hydrophobic Units Using Surface Plasmon Resonance Imaging

Abstract

Effective screening methods for the development of glycopolymers as molecular recognition materials are desirable for the discovery of novel biofunctional materials. A glycopolymer library was prepared to obtain guidelines for the design of glycopolymers for the recognition of cholera toxin B subunits (CTB). Glycopolymers with varying ratios of hydrophobic and sugar units were synthesized by reversible addition fragmentation chain transfer polymerization. N-tert-Butylacrylamide, N-phenylacrylamide, and N-cyclohexylacrylamide as hydrophobic units were copolymerized in the polymer backbone, and galactose, which contributes to CTB recognition, was introduced into the side chains by “post-click” chemistry. The thiol-terminated glycopolymers were immobilized on a gold surface. The polymer immobilization substrate was analyzed in terms of interaction with galactose recognition proteins (CTB, peanut agglutinin, and Ricinus communis agglutinin I) using surface plasmon resonance imaging. The polymers with high ratios of sugar and hydrophobic units had the strongest interactions with the CTB, which was different from the trend with peanut agglutinin and Ricinus communis agglutinin I. The binding constant of the CTB with the glycopolymer with hydrophobic units was 4.1 × 106 M–1, which was approximately eight times larger than that of the polymer without hydrophobic units. A correlation was observed between the log P value and the binding constant, indicating that the hydrophobic interaction played an important role in binding. New guidelines for the design of recognition materials were obtained by our screening method.

Facile Preparation of a Glycopolymer Library by PET-RAFT Polymerization for Screening the Polymer Structures of GM1 Mimics

“…The hydrophobicity of the functional groups of the co-monomers was quantified by the log P value, and the SPRI signals of the glycopolymers with 20% hydrophobic monomers for CTB showed a correlation with the log P values ( Figure 4 ). 15 This suggested that the hydrophobic groups with log P values higher than 0.15 exhibited a cooperative effect in binding to the pockets of CTB, resulting in enhanced interactions on the glycopolymer-immobilized surface. However, the correlation between the SPRI signals and the log P values was not observed for a lower co-monomer incorporation ratio (10%) due to the insufficient amount for the interactions with the binding pockets of CTB ( Figure S4 ).…”

“…The mixture of glycomonomer (GalAAm), AAm, and each hydrophobic monomer (EthylAAm, NIPAm, TBAm, ButylAAm, CyHexAAm, and PhAAm) were polymerized using PET-RAFT polymerization as per previous studies. 15 Setting the monomer concentration to 0.5 M, the monomers, RAFT agent (MCEBTTC), and photocatalyst (ZnTPP) were dissolved in DMSO (200 μL) at a molar ratio of 100:1:0.02. The mixtures of various monomer compositions were put in wells of the 96-well plate and were irradiated by LED lights (λ = 527 nm) at room temperature for 5 h. The conversion rates were determined by 1 H NMR, and the relative molecular weights and polydispersity index were calculated by gel permeation chromatography analysis.…”

“…Thus, screening of the polymer structures from many candidates (a glycopolymer library) is necessary to determine the effective polymer composition. 15 However, synthesis of the glycopolymers requires heating and degassing, making the library preparation time-consuming. Boyer and co-workers developed oxygen-tolerance radical polymerization techniques (photoinduced electron/energy transfer reversible addition–fragmentation chain-transfer polymerization; PET-RAFT polymerization) and enabled the preparation of well-defined synthetic polymers in an open-air environment.…”

Targeting Multiple Binding Sites on Cholera Toxin B with Glycomimetic Polymers Promotes the Formation of Protein–Polymer Aggregates

“…We assume that this difference is due to the sugar display on a flexible, cylinder backbone that supports extended structures and thus cross-linked aggregates form. The greater hydrophobicity of the norbornene-based glycopolymers may also play an important role in the binding of CTB to glycopolymers …”

“…The greater hydrophobicity of the norbornene-based glycopolymers may also play an important role in the binding of CTB to glycopolymers. 42 To explain the trend we observed, we propose the model system shown in Figure 5. In this system, the ligands of the glycopolymer point radially outward to maximize surface tension (Figure 1B).…”