Abstract
The antibacterial activity of immune-related peptides, identified by a differential gene expression analysis, was investigated to suggest novel antibacterial peptides. A cDNA encoding a defensin-like peptide, Coprisin, was isolated from bacteria-immunized dung beetle, Copris tripartitus, by using differential dot blot hybridization. Northern blot analysis showed that Coprisin mRNA was up-regulated from 4 hours after bacteria injection and its expression level was reached a peak at 16 hours. The deduced amino acid sequence of Coprisin was composed of 80 amino acids with a predicted molecular weight of 8.6 kDa and a pI of 8.7. The amino acid sequence of mature Coprisin was found to be 79.1% and 67.4% identical to those of defensin-like peptides of Anomala cuprea and Allomyrina dichotoma, respectively. We also investigated active sequences of Coprisin by using amino acid modification. The result showed that the 9-mer peptide, LLCIALRKK-NH2, exhibited potent antibacterial activities against Escherichia coli and Staphylococcus aureus.
Highlights
Antibacterial peptides play important roles in the innate immune systems of vertebrates and invertebrates
In addition to defense responses in the circulatory system, antimicrobial peptides are synthesized as effector molecules in epithelial and midgut tissues, which form a critical interface from the external environment [9,10,11]
The C. tripartitus larvae were cooled on ice and individually injected with 50 μL of E. coli JM109 (5 × 105 cells) suspended in physiological saline (150 mM NaCl/5 mM KCl)
Summary
Antibacterial peptides play important roles in the innate immune systems of vertebrates and invertebrates. The field of innate immunity in invertebrates, especially the study of particular insects, has revealed the importance of antimicrobial peptides in their defense systems. Most of the peptides are produced in the fat body or haemocytes and released into the hemolymph of insects [1,2,3] They are known to play important roles in humoral defense reactions [4,5,6,7,8]. We constructed a full-length cDNA library from bacteriaimmunized C. tripartitus and selected up-regulated clones using differential screening by a dot blot hybridization analysis. One of these up-regulated clones was isolated and characterized. This is the first report of the isolation and characterization of the defensin-like peptide, Coprisin, from the dung beetle, C. tripartitus
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