Correlation between Molecular Weight and Branch Structure of Glycopolymers Stars and Their Binding to Lectins

It has been hypothesized that maximum binding of carbohydrates can be achieved when the distance between two carbohydrate units are equivalent to two binding sites of a lectin. Therefore, a library of glyco starpolymers was prepared using RAFT polymerization to study the interaction with Concanavalin A (Con A). The starpolymers had a block structure in each arm and were composed of poly(2-acryloylethyl-2',3',4',6'-tetra-O-acetyl-alpha-d-mannopyranoside) (PMEA) as the outer block and the inactive, but water-soluble, poly(2-hydroxyethyl acrylate) (PHEA) as the inner block. The sizes of the starpolymers were determined using dynamic light scattering and hydrodynamic diameters between 3 and 12 nm in buffer solution were measured, which match the distance between two binding pockets of 6.5 nm ( Chem. Rev. 2002, 102, 555). Turbidity assay, precipitation assay, surface plasmon resonance and quartz crystal microbalance were employed to investigate the binding of the polymers with Con A. The effect of the molecular weight of PHEA, which is located in the core of the star, was found to contribute to chain stretching allowing the interaction with more Con A molecules. Longer PMEA blocks showed a lower binding efficiency per mannose functionality than shorter blocks. It was found that the initial diameter of the polymer in solution does not play a role in determining the binding efficiency. The measured amount of Con A conjugated per star polymer suggests that during the process the chains stretch significantly to accommodate a maximum amount of Con A.