Binding and stability properties of PEG2000 to globular proteins: The case of lysozyme

Abstract

• Lysozyme-PEG interaction was studied using calorimetry and spectroscopic techniques. • A PEG/lysozyme interaction in the low polymer concentration regime occurs. • The interaction process is weak, and it is entropically driven. • At low concentration, PEG induces an increase of the denaturation temperature. Poly(ethylene glycol) is a linear polymer widely used in many biotechnological and industrial applications. It is thought that PEG is an inert polymer and its effect on protein stability and dynamics is essentially due to the excluded volume effect which depends on its concentration. However, increasing evidence suggests that direct interactions can be established between PEG and proteins. With the aim to shed more light on PEG-protein interactions, this work evaluated the enthalpy pair interaction coefficient and the enthalpy cross-interaction coefficient for the system PEG2000-lysozyme. In addition, using calorimetry and spectroscopy, the binding, the stability and the conformational behaviour of lysozyme were evaluated in the low polymer concentration regime. We found that a weak interaction between lysozyme and PEG occurs with a binding constant of 1600 ± 230 M −1 . The interaction process is mainly entropically driven: the release of water molecules associated to protein surface and polymer chains may account for this phenomenon. In addition, we found that the general lysozyme structure was only marginally affected by PEG interaction. A small but significant increase in the denaturation temperature was observed most likely due to weak interactions with the polymer and to the dehydration of protein surface.