Expression,oxidative refolding,and characterization of six-histidine-tagged recombinant human LECT2, a 16-kDa chemotactic protein with three disulfide bonds

Human LECT2 is a 16-kDa chemotactic protein that consists of 133 amino acids and three intramolecular disulfide bonds. Here, we present the oxidative refolding of (His)(6)-LECT2, an N-terminally (His)(6)-tagged recombinant protein of human LECT2. (His)(6)-LECT2 was overproduced in Escherichia coli in the form of insoluble aggregates, solubilized with 8 M urea in the presence of 10 mM DTT, and purified and refolded on Ni-NTA agarose by lowering the urea concentration before the elution. This process, however, gave a mixture of oligomers of (His)(6)-LECT2 as well as the monomer, whose composition was as low as 36%. The oligomers formed as a result of incorrect intermolecular disulfide bonds. After the refolding on Ni-NTA agarose (step 1), the disulfide bonds were shuffled using a glutathione redox buffer (step 2) and the remaining thiols were completely oxidized (step 3) to improve the yield of correctly folded, monomeric (His)(6)-LECT2. The monomer composition was significantly improved to 81% by the three-step refolding method and the monomer thus obtained was shown to have the same conformation as the authentic LECT2 produced in CHO cells by CD and NMR spectroscopies. The yield of (His)(6)-LECT2 was 1.0 mg/L E. coli culture and was 16 times as high as that in our previous report, in which (His)(6)-LECT2 was purified from the soluble fractions of E. coli cell lysates.