Protein separation using non-ionic and cationic surfactant precipitation

Abstract

BACKGROUND: The predominant use of anionic surfactants to precipitate high isoelectric point (pI) proteins has increased in recent years, simplifying downstream separations. However, few researchers have tested cationic and non-ionic surfactants, whose properties are more desirable. This paper examines the effect of these surfactants on the precipitation efficiency of lysozyme, trypsin inhibitor and bovine serum albumin (BSA). RESULTS: Precipitation of BSA and trypsin inhibitor using the cationics, trioctylmethylammonium chloride (TOMAC) and dimethyl dioctadecyl ammonium chloride (DODMAC) was evaluated, with TOMAC being superior. More than 90% of BSA was precipitated using TOMAC at pH 9.0 with a molar ratio of surfactant/protein (R) of 100:1, while 88% was precipitated using DODMAC. However, for trypsin inhibitor, only 58% was precipitated at an R of 61:1 and pH 6.2 using TOMAC. Protein precipitate recovery using the anionic surfactant sodium bis-[2-ethylhexyl] sulfosuccinate (AOT) was effective only with trypsin inhibitor, with 100% of the protein being recovered. CONCLUSIONS: This study shows the potential of cationics to precipitate low pI proteins, and recover them using the counterionic surfactant AOT, with 100% recovery of trypsin inhibitor. However, non-ionic surfactants were ineffective. The method not only separates, but also preserves protein structure; hence cationic surfactants for low pI protein separation are promising.