Extraction of Human IgG in Thermo-Responsive Aqueous Two-Phase Systems: Assessment of Structural Stability by Circular Dichroism

Abstract

The structural stability of human IgG was studied throughout the extraction process with thermo-responsive UCON/dextran aqueous two-phase systems. Systems composed by 8% UCON and 5% dextran were assessed in both acetate pH 5 and phosphate pH 7. The extraction of IgG to the top phase was found to be favored at pH 5 reaching 85% yield with UCON 50HB-3520. During the extraction process conducted at 25°C no alteration in the secondary structure, evaluated by circular dichroism, was observed. The back-extraction step was induced by the thermo-precipitation of the UCON polymers at 59°C. At both pH values, mild changes in the secondary structure of IgG were observed for the 50HB-3520 and 50HB-5100 polymers while 50HB-2000 showed an increase in β-sheet content. The overall yield of the process was as high as 82% determined for the UCON 50HB-3520 system at pH 5.

Keywords:

• aqueous two-phase system
• circular dichroism
• immunoglobulin G
• temperature sensitive polymers

Abbreviations:

• ATPS, aqueous two-phase systems
• CD, circular dichroism
• PEG, polyethylene glycol

ACKNOWLEDGEMENTS

L. Borlido acknowledges Fundação para a Ciência e Tecnologia for the PhD fellowship BD/45077/2008. A. M. Azevedo acknowledges the program “Ciência 2007” of the Portuguese Ministry for Science, Technology and Higher Education.