Functional Diversity of Anti-Lipopolysaccharide Factor Isoforms in Shrimp and Their Characters Related to Antiviral Activity

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.

Antimicrobial proteins: From old proteins, new tricks

“…The authors incubated WSSV with synthetic domains before injecting the WSSV into the white prawn, Exopalaemon carinicauda, and then quantified the copy number. By substituting other amino acids for lysine, the authors demonstrated that the presence of lysine on the binding domain is essential for inhibiting the replication of the virus (Li et al, 2015). Both studies support the notion that ALF could, indeed, be a candidate antiviral agent but further work needs to undertaken on the exact way by which ALFs interfere with viral replication.…”

“…It is unclear how ALF interacts with WSSV but a plausible explanation might be virus-binding, which would prevent them from attaching and entering their host cell. More recent work by Li et al (2015) tested the inhibitory activity of synthetic lipopolysaccharide binding domains from F. chinensis ALF (Group B) against WSSV. The authors incubated WSSV with synthetic domains before injecting the WSSV into the white prawn, Exopalaemon carinicauda, and then quantified the copy number.…”

Antimicrobial and Antitumor Activities of Novel Peptides Derived from the Lipopolysaccharide- and β-1,3-Glucan Binding Protein of the Pacific Abalone Haliotis discus hannai

“…The synthetic loop of the LPS-binding domain from the ALFs of mud crab [8], shrimp [9,11,12], and Indian mud crab [10] inhibit both gram-negative and gram-positive bacteria, while that from the ALF of black tiger shrimp protects hematopoietic cell cultures from white spot syndrome virus infection [23]. Li et al [13] had compared antibacterial and antiviral activities of the LPS-binding domain of seven ALF isoforms from the Chinese shrimp and revealed that an identical Lys residue site was specifically conserved in peptide with antimicrobial activity, suggesting that a certain Lys residue is a key residue in antimicrobial activity.…”

“…For example, the corresponding synthetic LPS-binding domain peptides of anti-LPS factor (ALF) from several crustacean species were shown to exhibit antimicrobial activities [8,9,10,11,12,13]. Lactoferrin is a non-hemic iron-binding glycoprotein with antimicrobial activity via its LPS-binding domain (reviewed by [14]).…”

Structure and Bioactivity of a Modified Peptide Derived from the LPS-Binding Domain of an Anti-Lipopolysaccharide Factor (ALF) of Shrimp

“…The LPS binding domain (LBD) is considered as the functional domain for antimicrobial and antiviral activities [ 23 , 24 ]. Multiple isoforms of LBDs exhibit different antimicrobial activities against either Gram-positive or Gram-negative bacteria [ 25 , 26 ]. The LBD motif of rALF- Pm3 shows a β-hairpin structure with two anti-parallel β-strands linking by a disulfide bond [ 27 ].…”