Poly(Etyhlene Glycol)-Protein Interaction in Salt Containing Aqueous Solutions

Abstract

Poly(ethylene glycol) (PEG) is a common polymer in aqueous two-phase systems, and it is also used in other fields of biology, e.g. (i) protein precipitation, (ii) for creation of biocompatible surfaces, (iii) for in vitro stabilization of proteins, and (iv) as a refolding enhancer. Although a general picture of the features governing protein partition in PEG/salt aqueous two-phase systems can be given, the molecular mechanisms behind it are poorly understood. There is need for partition experiments performed with well characterized model peptides and proteins. We have developed a concept where we are using genetic engineering to modify a staphylococcal protein A derivative, ZZ0, with respect to its content of different short peptide units, e.g. like AlaTrpTrpPro and AlaIleIlePro. We are particularly interested in the use of these protein derivatives and free short peptides for the study of the molecular mechanisms involved in the PEG-protein interaction. Several techniques can be used to probe PEG-free peptide and PEG-protein interactions, not only in bulk solution, but also at solid surfaces. In this paper we will describe results from partition in PEG/potassium phosphate aqueous two-phase systems, and interaction with PEG coated surfaces. For the latter measurements we have applied: (i) retention studies on packed bed chromatography columns, and (ii) ellipsometry.