Crustacean Immunity

Abstract

We report here the isolation from plasma of two penaeid shrimp species of novel peptides/polypeptides with exclusive antifungal activities. A set of three molecules was purified with molecular masses at 2.7 kDa (Penaeus vannamei), 7.9 kDa, and 8.3 kDa (Penaeus stylirostris). Primary structure determination was performed by a combination of Edman degradation and mass spectrometry. The peptides display 95-100% sequence identity with a C-terminal sequence of hemocyanin, indicating that they are cleaved fragments of the shrimp respiratory protein. Specific immunodetection of the hemocyanin-derived (poly)peptides revealed that experimental microbial infections increase their relative concentration in plasma as compared with nonstimulated animals. Thus, the production of antifungal (poly)peptides by limited proteolysis of hemocyanin could be relevant to a shrimp immune reaction that would confer a new function to the multifunctional respiratory pigment of crustaceans.Penaeid shrimp production is a worldwide economic activity primarily important for intertropical developing countries. The intensification of shrimp farming over the last few decades has been accompanied by the development of infectious diseases from viral, bacterial, and, in some cases, fungal origin (1, 2). Therefore, a better understanding of penaeid shrimp immune response should help in the design of more efficient strategies for disease control.As for other invertebrates, cellular and humoral mechanisms contribute to the shrimp defense reaction by limiting microbial invasions or by helping the clearance/killing of the invading microbes from the blood and tissues (3-5). In particular, part of the innate immune response relies on the production of cationic antimicrobial peptides (6). Widespread in the living kingdom, these effectors have been well studied in insects and vertebrates in terms of structure, mode of action, and gene expression (7). We have recently isolated from the hemolymph of the shrimp Penaeus vannamei such a family of antimicrobial peptides named penaeidins (8), active against fungi and bacteria (9). Synthesized in the hemocytes, they are partly released into the blood circulation in response to microbial stimulations (10).In an attempt to understand the immune capability of shrimp to fight microbial infections, we looked for other antimicrobial factors active against shrimp pathogens. This research was engaged on two shrimp species, P. vannamei and Penaeus stylirostris, with special interest in their plasma-soluble molecules.In this paper, we present the isolation and biochemical characterization of a set of strictly antifungal (poly)peptides. These molecules, which are shown to derive from the C-terminal sequence of hemocyanins, were identified in the plasma of both shrimp species. Their antimicrobial activity spectrum and the physiological significance of their generation during the immune response of shrimp were also investigated. MATERIALS AND METHODS Animals and Hemolymph CollectionJuvenile shrimp P. vannamei and P. stylirostris...

Processing of an Antibacterial Peptide from Hemocyanin of the Freshwater Crayfish Pacifastacus leniusculus

“…The LPS injection results in the generation of other proteins than astacidin 1, whereas glucan injection mainly leads to production of astacidin 1. Recently, three kinds of small antimicrobial peptides were reported from shrimp, which could also be produced from the carboxyl-terminal part of hemocyanin (44). The production of these peptides can be enhanced by exposure to LPS.…”

Hemocyanin of the Molluscan Concholepas concholepas Exhibits an Unusual Heterodecameric Array of Subunits

“…We speculated that the nick site might generate a signal (molecular clock) to remove aged molecules from the hemolymph. Indeed, an exciting prospect would be that the nick in CCH could generate polypeptides exhibiting an antifungal and antimicrobial function, as described in shrimp (52). However, arthropod and molluscan hemocyanin are very different.…”

Antimicrobial peptides in marine invertebrate health and disease

“…Interestingly, crustacean haemocyanins release histidine-rich AMPs in response to microbial challenge [75,76]. In penaeid shrimp, strictly antifungal peptides are released from the C-terminus of haemocyanins [75]. Recently, the three-dimensional structure of the antifungal peptide PvHCt from L. vannamei was determined, and its mechanism of action was investigated.…”

“…Haemocyanins are respiratory proteins found in arthropods. Interestingly, crustacean haemocyanins release histidine-rich AMPs in response to microbial challenge [75,76]. In penaeid shrimp, strictly antifungal peptides are released from the C-terminus of haemocyanins [75].…”