| dc.description.abstract | Since the development of genetic engineering, protein and peptide drugs now play an important role in pharmaceutical industry. Unfortunately, a short circulating half-life time of protein/peptide drugs limits their pharmaceutical applications. A new product through grafting polyethylene glycol (PEG), a well-known biocompatible polymer, with protein/peptide drugs is called PEGylated product. The PEGylayed drug is able to avoid clearance of kidney or attack of immune system, thus prolong the circulating half-life time. This product is known as “Biobetters” which could improve the efficacy of biologics over the originals. However, the chromatographic purification process of PEGylation protein/peptide drugs is lacking of a general guidence. In particular, for the effects of PEG on protein/peptide drugs and PEG in solution on the chromatographic behavior are required for the guidence. In this study, we investigated the effects of buffer solution contains of the PEG molecules on the interaction between lysozyme and anionic resin (SP Sepharose) via thermodynamic analysis. By combining the analysis of isothermal titration calorimeter and adsorption isotherms, the results revealed that the bindings of lysozyme and resin both in saline buffer and in PEG-contained solution are dominated by enthalpy, indicating the binding adopts electrostatic interactions driven manner. Furthermore, we considered that the solution behavior of PEG on lysozyme-resin binding may be described as a “kosmotrope-like” polymer, which means the existence of PEG will facilitate the salting-out effect in the solution phase. In kosmotropic type saline buffer, such as ammonium sulfate, the addition of PEG molecules would facilitate the increase of binding affinity between lysozyme and resin which resulting in the decrease of binding entropy. Apparently, the hydration of PEG molecules reduces the tightly bounded water molecules around lysozyme surface to reduce the binding entropy gain, i.e. the hydration of PEG molecules lead to the less water molecules being repelled from the protein surface. On the contrary, the addition of PEG molecules would also facilitate the increase of binding affinity between lysozyme and resin which resulting in the increase of binding entropy in chaotropic salt, such as sodium chloride. We suggested that the PEG molecules may have a higher solubility in salting in solution; therefore, the tightly bounded water molecules still preserve around the lysozyme surface resulting in high entropic gain. Consequently, this study provided an important implication on the hydration role of PEG molecules to mediate the binding of protein on resin.
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