Role of polyethyleneimine in the purification of recombinant human tumour necrosis factor beta

Abstract

The chromatographic behaviour of recombinant human tumour necrosis factor beta (rhTNF-β) (pI ~9.0) during cation-exchange chromatography at pH 7.5 is investigated. Without prior treatment of the Escherichia coli cell extract with polyethyleneimine (PEI), very little rhTNF-β was bound to the column. However, upon addition of 5% PEI (100 μl ml-1) to the cell lysate, rhTNF-β was shown to bind to cation-exchange columns normally. TNF-β was readily precipitated from the clarified cell extract by 20% ammonium sulphate, but only ca. 25% of this precipitate could be re-solubilized for further purification. However, when 5% PEI was included in the solubilization buffer, the balance of the rhTNF-β could be recovered. It is proposed that charge interaction between rhTNF-β and nucleic acids in the cell extract is responsible for both of these anomalous phenomena, and that PEI (a cationic polyelectrolyte) was able to disrupt this interaction by displacing rhTNF-β from the charge complex.