title: The first chordate big defensin: identification, expression and bioactivity.
abstract: 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 α-helices, four β-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.
authors.affiliation: Department of Biology, Medical College of Qingdao University, Qingdao 266071, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Teng
authors.forename: Bei
authors.initials: B
authors.lastname: Gao
authors.forename: Shicui
authors.initials: S
authors.lastname: Zhang
mesh_terms: D000818:Animals; D001419:Bacteria; D001483:Base Sequence; D002816:Chordata, Nonvertebrate / Q000378:metabolism*; D003001:Cloning, Molecular; D018076:DNA, Complementary; D023082:Defensins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000276:immunology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D013682:Teichoic Acids / Q000494:pharmacology
chemical_list: D018076:DNA, Complementary; D023082:Defensins; D008070:Lipopolysaccharides; D013682:Teichoic Acids; C009900:lipoteichoic acid