Recombinant E. coli BL21 (DE3) strain harboring pET-6HGBP-H1a was cultivated in Luria-Bertani (LB) medium (10 g/L bacto-tryptone, 5 g/L yeast extract, and 5 g/L NaCl) supplemented with 100 µg/mL of ampicillin at 37 °C and 250 rpm. At OD 600 (DU600 ® Spectrophotometer, Beckman Coulter, Brea, CA, USA) of 0.4, cells were induced with 1 mM of isopropyl-β-D-thiogalactopyranoside (IPTG, Sigma) for the production of the fusion protein. After induction, cells were further cultured for 4 h. The cells were then harvested and disrupted by sonication (Braun Ultrasonics, Orlando, FL, USA) for 1 min at 20% output power. After centrifugation at 16,000× g for 10 min at 4 °C, the pellet containing the soluble protein fraction with high-level expressed target fusion-protein was collected for purification of the fusion protein. Because of the 6His tags, a HisTrap TM column (GE Healthcare, Chalfont St. Giles, UK) was used to purify the fusion protein without further purification steps. The protein concentration was determined by the Bradford assay with bovine serum albumin (BSA) as a standard.