Identification of duck liver-expressed antimicrobial peptide 2 (LEAP-2) and characterization of its bactericidal activity.

Objective: This study was conducted to identify duck liver-expressed antimicrobial peptide 2 (LEAP-2) and demonstrate its antimicrobial activity against various pathogens.

Methods: Tissue samples were collected from 6-8-week-old Pekin duck (Anas platyrhynchos domesticus), total RNA was extracted and cDNA was synthesized. To confirm the duck LEAP-2 transcript expression levels, qRT-PCR was conducted. Two kinds of peptides (a linear peptide and a disulfide-type peptide) were synthesized to compare the antimicrobial activity. Then, antimicrobial activity assay and fluorescence microscopic analysis were conducted to demonstrate duck LEAP-2 bactericidal activity.

Results: The duck LEAP-2 peptide sequence showed high identity with those of other avian species (>85%), as well as more than 55% of identity with mammalian sequences. LEAP-2 mRNA was highly expressed in the liver with duodenum next, and then followed by lung, spleen, bursa and jejunum and was the lowest in the muscle. Both of LEAP-2 peptides efficiently killed bacteria, although the disulfide-type LEAP-2 showed more powerful bactericidal activity. Also, Gram-positive bacteria was more susceptible to duck LEAP-2 than Gram-negative bacteria. Using microscopy, we confirmed that LEAP-2 peptides could kill bacteria by disrupting the bacterial cell envelope.

Conclusion: Duck LEAP-2 showed its antimicrobial activity against both Gram-positive and Gram-negative bacteria. In particular, disulfide bonds were important for a powerful killing effect by disrupting the bacterial cell envelope. Therefore, duck LEAP-2 can be used for effective antibiotics alternatives.