Binding of Lysozyme to Spherical Poly(styrenesulfonate) Gels.

Martin Andersson,Per Hansson

doi:10.3390/gels4010009

Abstract

Polyelectrolyte gels are useful as carriers of proteins and other biomacromolecules in, e.g., drug delivery. The rational design of such systems requires knowledge about how the binding and release are affected by electrostatic and hydrophobic interactions between the components. To this end we have investigated the uptake of lysozyme by weakly crosslinked spherical poly(styrenesulfonate) (PSS) microgels and macrogels by means of micromanipulator assisted light microscopy and small angle X-ray scattering (SAXS) in an aqueous environment. The results show that the binding process is an order of magnitude slower than for cytochrome c and for lysozyme binding to sodium polyacrylate gels under the same conditions. This is attributed to the formation of very dense protein-rich shells in the outer layers of the microgels with low permeability to the protein. The shells in macrogels contain 60 wt % water and nearly charge stoichiometric amounts of lysozyme and PSS in the form of dense complexes of radius 8 nm comprising 30–60 lysozyme molecules. With support from kinetic modelling results we propose that the rate of protein binding and the relaxation rate of the microgel are controlled by the protein mass transport through the shell, which is strongly affected by hydrophobic and electrostatic interactions. The mechanism explains, in turn, an observed dependence of the diffusion rate on the apparent degree of crosslinking of the networks.

Highlights

Complex formation between proteins and polyelectrolytes of opposite charge in aqueous solution has been a topic of scientific interest since the middle of the last century, arising from the need to develop methods for protein separation [1]
In the present paper we investigate this further by studying the binding of lysozyme to sodium poly(styrenesulfonate) (PSS) microgel spheres by means of micropipette-assisted microscopy
The interaction between lysozyme and PSS gels leads to the formation of dense complexes between the protein and the network chains

Summary

Introduction

Complex formation between proteins and polyelectrolytes of opposite charge in aqueous solution has been a topic of scientific interest since the middle of the last century, arising from the need to develop methods for protein separation [1]. Other important factors are polyion chain stiffness [9] and linear charge density [10], the net charge and distribution of charges [11] and hydrophobic patches on the protein surface [2], factors that may influence both the polyion–protein and protein–protein interactions. The present paper deals with the interaction between responsive polyelectrolyte networks of microscopic/mesoscopic size (50–100 μm) and proteins of opposite charge. Our interest in such systems derives both from their tentative use as drug delivery systems [12,13] and from intriguing biological phenomena, such as protein-assembly/sorting mediated by polyelectrolyte networks in protein secreting cells [14,15]

Methods

Results

Conclusion