GAP-initiated constitutive expression of a novel plectasin-derived peptide MP1106 by Pichia pastoris and its activity against Streptococcus suis

• Constitutive expression of rMP1106 by Pichia pastoris.
• Higher production rate of rMP1106 from the GAP promoter.
• Lower costs, risks and toxicity than AOX promoter depending on methanol induction during expression.
• Stronger antimicrobial activity of rMP1106 against Streptococcus suis than plectasin or antibiotics.
• High stability of rMP1106 in a broad range of pH, temperature and ionic strength.

MP1106 is a novel variant of plectasin with potent activity against some Gram-positive pathogenic bacteria, especially for Streptococcus suis and Staphylococcus aureus. MP1106 was successfully expressed in Pichia pastoris X-33 using the glyceraldehyde-3-phosphate dehydrogenase (GAP) promoter. The total protein concentration and antimicrobial activity were 998.3 mg/L and 51,200 AU/mL, respectively. After purification by cation exchange chromatography, recombinant MP1106 (rMP1106) with a concentration of 100.13 mg/L and a purity of 95.2% was obtained from fermentation culture. Its antimicrobial spectrum was similar to that of plectasin, and the antibacterial activity against S. suis CVCC3309 was enhanced up to 29-fold over that of plectasin. In addition, 97.9% of the S. suis CVCC606 bacteria were killed by 16× minimal inhibitory concentration (MIC) rMP1106 within 6 h. The percentage hemolysis by rMP1106 against mouse erythrocytes was 3.8% at a concentration of 512 μg/mL. Exposure of porcine intestinal epithelial cells to 16–128 μg/mL rMP1106 caused a 9.5% decrease in cell viability. The rMP1106 was stable over broad ranges of temperature, pH and NaCl concentration. In addition, rMP1106 was highly resistant to papain, proteinase K and snailase digestion but susceptible to trypsin and slightly susceptible to pepsin. These results suggested that rMP1106 has potential as a promising therapeutic drug against S. suis infections.