Protein refolding at high concentrations using detergent/phospholipid mixtures

Refolding of the sulfurtransferase enzyme rhodanese (EC 2.8.1.1) at high concentrations (0.2 mg/ml) was obtained at significant yields (≥45%) by using mixtures composed of detergents (either Triton X-100 or lauryl maltoside) and phospholipids. It is presumed that the ratio of detergent to phospholipid used in these mixtures results in the formation of very large micellar structures. Protein folding at lower concentrations (0.02 mg/ml) gave high yields (94%) when using the Triton X-100/phosphatidylglycerol micelle and these yields were higher than those obtained with either detergents or chaperonins. Differences between mixed micelle and liposome-mediated protein folding were clarified. We postulate that the method described here is successful at preventing misfolding and/or aggregation, and promoting correct folding, because the mixed micelle has both polar and nonpolar moieties which can bind to various exposed interactive sites in either unfolded proteins or protein folding intermediates. In this report, we detail the factors that allow the recovery of large amounts of active protein. This methodology should facilitate the large-scale production of biologically active, medically important proteins.