Fusion Partner Facilitates Expression of Cell-Penetrating Peptide L2 in Pichia pastoris

Background: L2 is formed by combining the pheromone of Streptococcus agalactiae (S. agalactiae) and a cell-penetrating peptide (CPP) with cell-penetrating selectivity. L2 has more significant penetration and better specificity for killing S. agalactiae. However, the production of AMPs by chemical synthesis is always a challenge because of the production cost. Methods: This study was devoted to the heterologous expression of the cell-penetrating peptide L2 in Pichia pastoris using SUMO and a short acidic fusion tag as fusion partners, and the high-density expression of SUMO-L2 was achieved in a 5 L fermenter. Results: The results showed that SUMO-L2 expression in the 5 L fermenter reached 629 mg/L. The antibacterial activity of recombinant L2 was examined; the minimum inhibitory concentration (MICs) and minimum bactericidal concentration (MBCs) of purified L2 were 4–8 μg/mL and 8–16 μg/mL against S. agalactiae after 84 h of lysis with 50% formic acid. Conclusions: The findings suggest that SUMO is a suitable fusion tag to express cell-penetrating peptide L2.