Identification and characterization of SaRpAMP, a 60S ribosomal protein L27-derived antimicrobial peptide from amur catfish, Silurus asotus.

Aquatic freshwater fish like catfish, Silurus asotus , lives in microbe-rich environments, which enable this fish to develop necessary defense mechanisms. Antimicrobial peptides, along with other innate immune factors, are regarded as an important group in this defense. An antimicrobial peptide, which was isolated from the skin of S. asotus , was identified as a C-terminal fragment of 60S ribosomal protein L27 from S. asotus. The peptide was, then, designated Silurus asotus 60S ribosomal protein L27-derived antimicrobial peptide, Sa RpAMP. Primary structure analyses and cDNA cloning revealed that Sa RpAMP was 4185.36 Da and composed of 33 amino acids (AAs). Its precursor had a total of 136 AAs containing a pro-sequence of 103 AAs encoded by the nucleotide sequence of 512 bp that comprises a 5′ untranslated region (UTR) of 32 bp, an open reading frame (ORF) of 411 bp, and a 3′ UTR of 69 bp. Secondary structure analyses showed that Sa RpAMP had two α-helices with turns and coils and an amphiphilic structure, a finding consistent with the 3D model of the peptide. Sa RpAMP exhibited potent antibacterial activity comparable to piscidin 1, a powerful positive control. Its antimicrobial activity against fungus C. albicans was relatively weak. The antimicrobial activity of Sa RpAMP was not diminished by heat treatment and changes in pH but was abolished by proteolytic enzyme digestion. Membrane permeability assays suggested that Sa RpAMP interacts with both the outer and inner bacterial membranes. This was consistent with the results of lipid titration and quenching of Trp fluorescence that demonstrated Sa RpAMP's interaction with acidic liposomes. Collectively, these findings suggest that the identified peptide, Sa RpAMP, was the first antimicrobial peptide reported to be derived from the C-terminal region of 60S ribosomal protein L27. The findings also suggest that the action mechanism of Sa RpAMP involved the interaction of the peptide with the bacterial membranes. • An antimicrobial peptide (Sa RpAMP) identical to the C-terminus of 60S ribosomal protein L27 was identified from S. asotus. • Sa RpAMP was a cationic alpha-helical antimicrobial peptide with potent antimicrobial activity. • Sa RpAMP permeabilizes bacterial and artificial membranes. • Membrane interaction is involved in the action mechanism of Sa RpAMP. [ABSTRACT FROM AUTHOR]