Oxidative refolding of Denatured/Reduced lysozyme utilizing the chaperone-like function of liposomes and immobilized liposome chromatography

Abstract

Oxidative refolding of the denatured/reduced lysozyme was examined in the presence of small unilamellar vesicles (SUVs) essentially composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). SUVs facilitated the recovery of the enzymatic activity of lysozyme like molecular chaperones through the interaction with the refolding intermediate of lysozyme. The highest reactivation yield (87%) was obtained by delaying oxidation time (15-30 s) after dilution of the denaturant concentration was initiated in the presence of SUVs. SUVs supplemented with 1 mol % phosphatidylethanolamine were covalently coupled to gel beads, and then the interactions of SUVs with lysozyme at the various conformations were quantitatively examined with immobilized liposome chromatography (ILC). The reduced lysozyme lacking disulfide bonds was found to have a property similar to that of the molten globule state in terms of its local hydrophobicity, which was determined with the aqueous two-phase partitioning method. The reduced lysozyme was more clearly retarded on the ILC column than the native and 1 M guanidinium hydrochloride (GuHCl)-treated lysozymes with intact disulfide bonds. Similar results were obtained for alpha-lactalbumin, which has three-dimensional structure closely similar to that of lysozyme, regarding the membrane-protein interaction. These results can be interpreted as follows. In the early stage of the oxidative refolding, liposomes bound to the refolding intermediate of lysozyme lacking disulfide bonds. Then, liposomes assisted the formation of the tertiary structure of lysozyme by reducing protein intermolecular interactions, which usually cause the formation of the inactive aggregates. Consequently, the correct formation of the disulfide bonds was promoted. On the basis of the above results, the chromatographic oxidative refolding was also examined with ILC. The denatured/reduced lysozyme (9 mg/mL, 10 &mgr;L) was passed through the ILC column with a flow rate of 1 mL/min, which corresponds to the retention of lysozyme about 1 min in the ILC column. Subsequent oxidation of the eluted lysozyme resulted in the almost complete recovery (100%) of the original enzymatic activity of lysozyme.