Molecular characterization and expression of a novel big defensin (Sb-BDef1) from ark shell, Scapharca broughtonii

• Published in: Fish & shellfish immunology 2012-11, Vol.33 (5), p.1167-1173
• Main Authors: Li, Meng, Zhu, Ling, Zhou, Chun-ya, Sun, Shan, Fan, Yan-jun, Zhuang, Zhi-meng
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Analysis of Variance; Animals; Base Sequence; Big defensin; Branchiostoma lanceolatum; Decapoda; Defensins - genetics; Defensins - metabolism; DNA Primers - genetics; DNA, Complementary - genetics; Expressed Sequence Tags; Gene Expression Profiling; Gene Expression Regulation - physiology; Gram-negative microbial challenge; Hepatopancreas - metabolism; Marine; Molecular Sequence Data; Mollusca; Open Reading Frames - genetics; Quantitative real-time PCR; Real-Time Polymerase Chain Reaction; Scapharca - genetics; Scapharca - immunology; Scapharca - microbiology; Scapharca broughtonii; Sequence Analysis, DNA; Time Factors; Tissue distribution; Vibrio; Vibrio - immunology
• ISSN: 1050-4648; 1095-9947
• DOI: 10.1016/j.fsi.2012.09.008

Big defensins, endogenous cysteine-rich antimicrobial peptides (AMPs) with antimicrobial activity and immunomodulatory property, play crucial roles in host defense against various microbial pathogens. A novel big defensin (Sb-BDef1) of ark shell Scapharca broughtonii was identified by expressed sequence tag (EST) and RACE techniques. The Sb-BDef1 cDNA contained an open reading frame (ORF) of 336-bp encoding a polypeptide of 111 amino acids with a putative signal peptide of 21 amino acid residues, followed by a putative propeptide of 11 residues and a putative mature peptide of 79 residues. The mature peptide shared the common features of big defensins, including a high hydrophobic residues region (59%) in the N-terminus, a defensin domain in the C-terminus, which perfectly corresponds to the six conserved disulfide-bonded cysteine residues involved in the formation of the internal disulfide bridges (C1–C5, C2–C4 and C3–C6) in all big defensins from mollusk, horseshoe crab and amphioxus. Quantitative real-time PCR analysis revealed that the expression of Sb-BDef1 transcript was detected in all the tissues examined from normal ark shells, and the temporal expression of Sb-BDef1 mRNA was remarkably up-regulated at 8, 16 h in hemocytes, and at 16, 24 h in hepatopancreas after Vibrio anguillarum-challenge, respectively. These results suggested that Sb-BDef1 was a constitutive and inducible acute-phase protein and should be involved in immune response of Gram-negative microbial infection in ark shell S. broughtonii. ► A novel big defensin of Scapharca broughtonii was identified and characterized. ► The Sb-BDef1 was detected in all the tissues examined from normal ark shells. ► The Sb-BDef1 was up-regulated in hemocytes and hepatopancreas by bacterial challenge.