Recombinant protein purification using thermoseparating aqueous two-phase systems
Abstract: The biotechnology industry has grown considerably over the past twenty years, and the revolution within the field of molecular biology has dramatically improved the possibilities of producing proteins and other important biomolecules. The product of interest will be obtained in a multi-component solution and some challenging purification work has to be performed to recover the target molecule in a pure form. The aim of this thesis is to show that an aqueous two-phase system composed of technical grade polymer(s) and recyclable polymers can be used as an efficient primary recovery step for biological material. The polymers studied are either low-cost starch derivatives or thermoseparating copolymers, e.g. ethylene oxide and propylene oxide random copolymers (EOPO polymers). Thermoseparating polymers in water solution will upon heating form a two-phase system where one phase is enriched in polymer and the other depleted. The thermoseparating polymer can be recycled and used in a number of extraction systems. Apolipoprotein A-I (Apo A-I) was chosen as target protein in this study. The protein was purified from cell-free E. coli extracts. Systems composed of EOPO/hydroxypropyl starch had high protein capacity and Apo A-I could be efficiently purified while retaining a high yield. Due to the amphiphilic properties of Apo A-I the purification of the protein could be improved by addition of surfactant. Recycling of thermoseparating polymers has been performed, and the recycled polymers have been shown to be just as efficient for protein purification as fresh polymers.
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