Abstract
Penaeidins are members of a special family of antimicrobial peptide existing in penaeid shrimp and play an important role in the immunological defense of shrimp. Here, we report a penaeidin sequence cloned from the Indian white shrimp Fenneropenaus indicus (Fein-Penaeidin). The Fein-Penaeidin open reading frame encodes a 77 amino acid peptide including a 19 amino acid signal peptide. The deduced amino acid sequences of Fein-Penaeidin include a proline rich N-terminal domain and a carboxyl-domain that contains six cysteine residues. Structural analysis revealed an alpha-helix in its secondary structure and the predicted 3D structure indicated two-disulphide bridges in the alpha-helix. Phylogenetic analysis and sequence comparison with other known peaneidin suggest the gene shows high similarity to that of penaeidin from Peneaus monodon (95%), F. indicus (80%) and Fenneropenaeus chinensis (74%). Fein-Penaeidin was examined in normal and microbial challenged shrimp and was found to be constitutively expressed in haemocytes, Heart, gills, muscles, intestine, hepatopancreas and eyestalk. Bacterial challenge resulted in mRNA up-regulation, inducing expression at 6 h post injection indicating the penaeidin involved in the innate immunity.