A new type antimicrobial peptide astacidin functions in antibacterial immune response in red swamp crayfish Procambarus clarkii

A new antibacterial peptide called astacidin was characterized from hemocytes of red swamp crayfish Procambarus clarkii, and designated as PcAst. The full-length cDNA of PcAst contained 828 nucleotides with a polyadenylation sequence and a poly-A tail. PcAst encoded a peptide of 43 amino acids, with a signal peptide of 23 amino acids. The mature peptide contained 20 amino acids, among which four were proline/arginine amino acids. Similarity analysis showed that PcAst shared high identity with astacidin 2 from freshwater crayfish Pacifastacus leniusculus. Quantitative real-time PCR analysis showed that PcAst transcripts were mainly distributed in hemocytes and gills. The time-course expression analysis showed that after Vibrio anguillarum and Staphylococcus aureus injection, the transcripts of PcAst were upregulated in the gills. The synthetic small peptide for mature PcAst displayed inhibitory activity against the growth of some Gram-positive and Gram-negative bacteria. This peptide also had a binding ability to bacterial cell wall components, including peptidoglycan, lipopolysaccharide and lipoteichoic acid. PcAst functioned in the bacterial clearance immune reaction after V. anguillarum and S. aureus infection. These results indicate that PcAst has an important function in antibacterial innate immune response in red swamp crayfish P. clarkii.