High-level expression of human β-defensin-2 gene with rare codons in E-coli cell-free system

Human beta-defensin-2 (hBD2) is a small cationic peptide with a broad range of antimicrobial activity. An E. coli cell-free system was employed to express the hBD2 fusion protein by using the hBD2 gene with 14 rare codons. The results showed that the expression level of trxA-hBD2 fusion protein was 0.35 mg/ml, which is the same as that obtained with a synthetic codon-optimized gene. By using another fusion partner (GFP), similar high-level expression was also achieved in this cell-free system. This meant that human beta-defensin-2 gene could be directly used to express hBD2 fusion protein efficiently in an E. coli cell-free system without the optimization of codons. The expression level of hBD2 fused with thioredoxin could be further improved up to 2.0 mg/ml by adopting a continuous exchange cell-free system. A simple one-stage affinity purification procedure was also developed to recover this fusion protein efficiently.