PenBase
Penaeidin database

     To date, the properties of penaeidins isolated from L. vannamei have been studied in details: Recombinant Litvan PEN2-1 and Litvan PEN3-1 have been produced in the yeast Saccharomyces cerevisiae and characterized (Destoumieux et al., 1999). In addition, Litvan PEN4-1 has been chemically synthetised and its antimicrobial activity spectrum determined (Cuthbertson et al. 2004). Very recently, Fenchi PEN3-1 has been succesfully produced in the yeast Pichia Pastoris and the recombinant peptide has been characterized (Li et al., 2005).

Antimicrobial activities
Litvan-PEN2-1, Litvan PEN3-1 and Litvan PEN4-1 have a broad-spectrum of antifungal activities against filamentous fungi with minimum inhibitory concentration (MIC) below 10µM (Table 1). Penaeidin antibacterial activity is predominantly directed against Gram-positive bacteria. Litvan PEN3-1 displays potent growth inhibition properties against various bacteria (MIC = 0.3-0.6 µM) and against filamentous fungi. Penaeidins also display in vitro a weak antibacterial activity against Gram-negative strains (up to 20 µM).

Table 1  : Antimicrobial spectrum of activity of the recombinant Litvan PEN2-1 and Litvan PEN3-1 (Destoumieux et al., 1999), the chemically synthetised Litvan PEN4-1 (Cuthbertson et al. 2004) and the recombinant Fenchi PEN3-1 (Li et al., 2005). MIC are expressed as the interval a-b, where a is the highest concentration tested at which the growth of the microorganism is not inhibited and b the lowest concentration that causes the 100% growth inhibition.

Chitin-binding
Chitin is one of the most abundant polysaccharide found in nature. It is a β-1,4-linked biopolymer of N-acetylglucosamine that is a component of the fungal and algal cell wall and it also forms the hard integument of arthropods. The C-terminal domain of penaeidins presents some similarities and partial conservation of a primary sequence motif common to several chitin-binding proteins isolated from plants and was shown to confer to the whole molecule an ability to attach chitin tighly. Penaeidin chitin-binding ability could participate both in antimicrobial activity and in wound healing and chitin assembly. The peptides may play a role in the protection of the animals during molting cycle when the animals are particularly exposed to potential infections. This dual function of penaeidins is likely determinant for the survival of the animals. To address this question, it is now underinvestigation whether the penaeidins conserve their antimicrobial activity when bound to the shrimp cuticle.

Opsonic and agglutinating activities
In vitro confrontation of L. vannamei hemocytes with Vibrio alginolyticus has revealed an opsonic property for penaeidins (Munoz et al. 2002). It is attractive to assume that in shrimp a mechanism mediated by penaeidins has been developed which discriminates between bacteria strains. Foreign microorganisms, such as Gram-positive bacteria or fungi, are susceptible to penaeidins antimicrobial activity at lower peptide concentration (MIC values ranging at 0.3-0.6 µM). Vibrionaceae strains, which can be commensal or belong to the shrimp internal microflora, would be opsonized or agglutinated. The agglutination of Vibrio bacteria may represent a mechanism adapted for the control of bacteria population density in the shrimp. However, the mechanisms by which penaeidins agglutinate the bacteria still require elucidation.