*3.1. Materials*

All the consumables used in the experiments were of analytical grade. Luria-Bertani broth, urea, sodium chloride, imidazole, Amicon Ultra10 K device, etc., were purchased from Merck (Darmstadt, Germany). Isopropyl-d-1-thiogalactopyranoside (IPTG) and Kanamycin were obtained from Sigma (Saint Louis, MO, USA). Ni-NTA beads were purchased from Qiagen, Hilden, Germany. The syringe filter (0.22 µm) was purchased from Millipore Corporation (Burlington, MA, USA).
