A codon-optimized gene encoding CafA (residues 75-287) of A. fumigatus was cloned between the EcoRI and NotI sites of the pGEX4T3 vector. This vector harbors a thrombin-cleavable N-terminal glutathione S-transferase. The resulting construct was transformed into Escherichia coli BL21 (DE3) cells, grown in Lysogeny Broth medium at 37°C. When the optical density at 600 nm (OD600) reached 0.6-0.7, protein expression was induced with 1 mM isopropyl-β-d-thiogalactopyranoside (IPTG) for 16 h at 20°C.
After harvesting cells and lysing using a microfluidizer, CafA protein was purified using glutathione agarose beads (GoldBio, USA). After thorough washing, the protein was eluted by on-column thrombin cleavage in buffer containing 20 mM TRIS-HCl pH 8.0 and 200 mM NaCl. The protein was further purified by HiTrap Q anion exchange chromatography (GE Healthcare, USA) and Superdex 200 gel filtration chromatography (GE Healthcare). All purification steps were performed on ice or at 4°C.
After harvesting cells and lysing using a microfluidizer, CafA protein was purified using glutathione agarose beads (GoldBio, USA). After thorough washing, the protein was eluted by on-column thrombin cleavage in buffer containing 20 mM TRIS-HCl pH 8.0 and 200 mM NaCl. The protein was further purified by HiTrap Q anion exchange chromatography (GE Healthcare, USA) and Superdex 200 gel filtration chromatography (GE Healthcare). All purification steps were performed on ice or at 4°C.