Journal
FISH & SHELLFISH IMMUNOLOGY
Volume 32, Issue 4, Pages 572-577Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.fsi.2012.01.007
Keywords
Protochordate; Amphioxus; Branchiostoma; Big defensin; Antimicrobial activity
Funding
- Ministry of Science and Technology (MOST) [2012CB114404, 31172071]
- Natural Science Foundation of China
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Defensins are broadly present in plants, invertebrates and vertebrates, but little information is available about it in amphioxus, a protochordate holding a key phylogenetic position. In this study, a big defensin cDNA was identified from the amphioxus Branchiostoma japonicum (termed Bjbd). The cDNA contained an open reading frame (ORF) of 354 bp encoding a 117 amino acid protein, which had an N-terminal signal sequence followed by a propeptide and the mature big defensin. The mature peptide had the hydrophobic region GAAAVT(A)AA at N-terminus and the consensus pattern C-X6-C-X3-C-X13(14)-C-X4-C-C at C-terminus as well as four alpha-helices, four beta-sheets, and three disulfide bridges (C1-C5, C2-C4 and C3-C6) in the predicted tertiary structure. This is the first big defensin gene ever identified in the phylum Chordata. Quantitative real-time PCR analysis revealed that Bjbd was constitutively expressed in most of the tissues examined, and its expression was remarkably up-regulated following the challenge with LPS, LTA, Aeromonas hydrophila and Staphylococcus aureus. Moreover, the recombinant BjBD was shown to be able to inhibit the growth of S. aureus, Escherichia coli and A. hydrophila. Taken together, these suggest that BjBD is a molecule involved in the removal of invading pathogens. (C) 2012 Elsevier Ltd. All rights reserved.
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