Abstract
Anti-lipopolysaccharide factor (ALF) is a small protein with broad-spectrum antimicrobial activity, which has potential application in the disease control. Previously, we isolated seven ALF isoforms from the Chinese shrimp Fenneropenaeus chinensis. In the present study, their distributions in tissues of shrimp were analyzed and the data showed that different isoforms had different expression profiles, which suggested that they might have different functions. Then, the functions of different isoforms were studied by analyzing the antibacterial and antiviral activities of the functional domain of ALFs, the LPS-binding domain (LBD), which were synthesized by chemical methods. Different ALFs showed distinct antibacterial and antiviral activities, which were consistent with their diverse tissue distribution patterns. Sequence analysis on the LBD domain of different isoforms revealed that an identical lysine residue site was specifically conserved in peptides with anti-WSSV activity. In order to confirm whether this lysine residue is critical to the antiviral activity of the peptide, new peptides were synthesized by changing residues at this site. Changing the lysine residue at the specific site to other amino acid residue, the antiviral activity of the peptide apparently decreased. While replacing other residue with a lysine residue at this site in LBD peptide without anti-WSSV activity, the peptide will obtain the antiviral activity to WSSV. These results not only showed us a comprehensive understanding on the function of ALFs from F. chinensis, but also provided clues for the development of ALFs as potential therapeutic drugs to WSSV.
Highlights
Anti-lipopolysaccharide factor (ALF) is a small protein with broad-spectrum antimicrobial activity, which has potential application in the disease control of shrimp
From Eriocheir sinensis, and PtALF from Portunus trituberculatus, have been reported to be expressed constitutively in hemocytes and up-regulated after bacteria challenges, which suggest that ALFs might play important roles in defense against bacterial pathogens [3,4,5,6,7,8]
In order to have a basic understanding on their potential function, tissue distribution of FcALFs was performed
Summary
Anti-lipopolysaccharide factor (ALF) is a small protein with broad-spectrum antimicrobial activity, which has potential application in the disease control of shrimp. The synthetic peptides corresponding to these LPS-binding domains, such as ALFSp, SsALF from Scylla paramamosain and Scylla serrata [17,20], and SALF55–76 from P. monodon [21] showed antibacterial activity against various bacteria. The synthetic LPS-binding domain from crayfish ALF could inhibit the replication of WSSV in cultured Hpt cells [11]. In P. trituberculatus, seven ALF isoforms were cloned and they displayed different biological activities [4,5,6,24,25]. The functions of different FcALFs will be analyzed comparatively These data will provide us a comprehensive understanding on the function of ALFs, and give an instruction for the development of therapeutic drugs to shrimp disease control
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