Structural, functional and phylogenetic analysis of a beta defensin gene from the Whipfin silverbiddy, Gerres filamentosus (Cuvier, 1829)

Abstract

Beta defensins have been considered as a major class of Antimicrobial peptides (AMPs) that play an important role in the innate immunity of fishes. In this study, we have identified and characterized a β-defensin gene sequence from the Whipfin silverbiddy, Gerres filamentosus which was termed as Gf-Def. The Gf-Def open reading frame (ORF) consists of 192 bp that encodes 63 amino acid residues. It includes a signal peptide region of 20 amino acids followed by a mature peptide sequence of 43 amino acids. Gerres filamentosus beta defensin (Gf-Def) has a molecular weight of 5.2 KDa and an isoelectric point of 8.90 with a GRAVY score of −0.872. Also, the characteristic six cysteine residues involved in pattern specific formation of intramolecular disulfide bridges could be deduced from the peptide sequence using Cys_Rec software. Three-dimensional modeling of Gf-Def carried out using DNASTAR protean software revealed β strands stabilized by cysteine sulfide bonds along with a short N-terminal α helix spanning the signal peptide sequence. Four Conserved motifs were identified in Gf-Def, all of which were unexceptionally and extensively shared by other fish defensins suggesting a possible functional similarity and evolutionary selection of the sequence. Phylogenetic analysis revealed that Gf-Def was close to Oplegnathus fasciatus, Siniperca chautsi, Trachinotus ovatus and Lates calcarifer defensins which probably suggests that Gf-Def peptide sequence is quite similar to β-defensin sequences of other Perciformes. This being the first report of a beta defensin from whipfin silverbiddy, G. filamentosus and the comparative analysis shall provide a background data for the functional and evolutionary studies on fish beta defensins.