AMPs provide an early and localized first line of defense against pathogens [2], [3] and [4]. Moreover, their small

size amphipathic structure and cationic character makes them easy to synthesize without dedicated cells or tissues, and they rapidly diffuse to the point of infection. The first antimicrobial peptide characterized was a 6.5 kDa proline peptide from the haemocytes of the shore crab Carcinus maenas [5]. Besides providing an immediate and broad spectrum of microbial activity, AMPs can kill bacteria in micro molar range, are promptly synthesized at low metabolic cost, easily stored in large amounts and are readily available shortly after an infection [6] and [7]. Penaeidins are members of selleck screening library a family of AMPs, originally isolated from the shrimp Litopenaeus vannamei, which posses Reverse Transcriptase inhibitor both Gram-positive antibacterial and antifungal activities [8]. It appears to be a family of AMPs ubiquitous among penaeid shrimp where they

are major components of the immune response synthesized and stored in granulocytes and released after stimulation [5], [9] and [10]. They are highly cationic molecules composed of a N-terminal proline-rich domain (PRD), followed by a C-terminal domain containing 6 conserved cysteine residues that form three disulfide bonds in a cysteine-rich domain (CRD) [11]. Recent studies report elucidates that thirty-nine penaeidins have been identified from eight different species of shrimp. These penaeidins are divided into five categories (penaeidin 1–5) based on the amino acid sequence similarities. Penaeidin-4, which is the most powerful bactericide among the penaeidins

[12], [13] and [14]. Modern research approaches are needed to compare the importance of penaeidin of the Indian white shrimp F. indicus with other molecular data available in the GenBank. Thus, the solution structure of pheromone Litvan PEN3-1 and Litvan PEN4-1 has been determined revealing the overall organization of the two domains and the arrangement of the disulfide bonds [15]. Amino acid sequence analysis of penaeidin indicates that the amphipathic structure is a part of the CRD and has more positively charged amino acids than PRD, suggesting that CRD may be the pathogen-recognition domain [5]. The PRD exhibits a cytokine function that regulates the granulocytes and semi-granulocytes adhesion by regulating the extracellular matrix (ECM) and cell adhesion molecules (CAMs) in the tiger shrimp. Based on this, it has been proposed that penaeidin is involved in the wound healing process in shrimp [16]. Shrimp are constantly exposed to a variety of bacteria and viruses in the aquatic environment. Vibriosis, commonly caused by Vibrio harveyi, Vibrio parahaemolyticus and Vibrio alginolyticus is the most predominant bacterial disease causing mass mortalities of cultured shrimp worldwide [17], [18] and [19].