Characterization and expression of a new subfamily member of penaeidin antimicrobial peptides (penaeidin 5) from Fenneropenaeus chinensis

Litopeidin28-51, a novel antimicrobial peptide from Litopenaeus vannamei, combats white spot syndrome virus infection through direct virus lysis and immunomodulatory effects

White spot syndrome virus (WSSV) poses a critical threat to crustacean aquaculture, particularly shrimp, causing widespread pandemics. In crustaceans, hemocytes function as a key component of the innate immune system and play a pivotal role in both cellular and humoral immune responses by producing various immune factors, such as antimicrobial peptides (AMPs), to defend against pathogenic microorganisms. In this study, an uncharacterized functional gene named Litopeidin was identified in Pacific white shrimp (Litopenaeus vannamei). It exhibited heightened expression in hemocytes and demonstrated a significant response to WSSV infection. Further, a truncated peptide, Litopeidin28-51, derived from this gene, was characterized and identified as a novel AMP with robust antibacterial and antifungal properties, especially against common aquatic pathogens, including Vibrio spp. Moreover, Litopeidin28-51 significantly suppressed the expression of viral genes (IE1 and VP28, WSSV replication-related genes) and the VP28 protein, as well as reduced viral copy numbers in hematopoietic tissue (Hpt) cells following WSSV infection. Mechanistic studies revealed that Litopeidin28-51 exhibited a direct virucidal effect on WSSV and significantly upregulated immune-related gene expression (including Relish, ALF, Crustin, and LYZ1) in Hpt cells. Notably, in Cherax quadricarinatus and L. vannamei, either co- or pre-treatment with Litopeidin28-51 markedly reduced animal mortality and viral replication in tissues. Collectively, the findings suggest that Litopeidin28-51, a newly identified AMP with potent antibacterial activity, effectively inhibits WSSV replication by disrupting the viral envelope and regulating the cellular antiviral responses, making it a promising candidate for developing anti-infective agents or immunostimulants in aquaculture.

Aquatic Invertebrate Antimicrobial Peptides in the Fight Against Aquaculture Pathogens

The intensification of aquaculture has escalated disease outbreaks and overuse of antibiotics, driving the global antimicrobial resistance (AMR) crisis. Antimicrobial peptides (AMPs) provide a promising alternative due to their rapid, broad-spectrum activity, low AMR risk, and additional bioactivities, including immunomodulatory, anticancer, and antifouling properties. AMPs derived from aquatic invertebrates, particularly marine-derived, are well-suited for aquaculture, offering enhanced stability in high-salinity environments. This study compiles and analyzes data from AMP databases and over 200 scientific sources, identifying approximately 350 AMPs derived from aquatic invertebrates, mostly cationic and α-helical, across 65 protein families. While in vitro assays highlight their potential, limited in vivo studies hinder practical application. These AMPs could serve as feed additives, therapeutic agents, or in genetic engineering approaches like CRISPR/Cas9-mediated transgenesis to enhance resilience of farmed species. Despite challenges such as stability, ecological impacts, and regulatory hurdles, advancements in peptidomimetics and genetic engineering hold significant promise. Future research should emphasize refining AMP enhancement techniques, expanding their diversity and bioactivity profiles, and prioritizing comprehensive in vivo evaluations. Harnessing the potential of AMPs represents a significant step forward on the path to aquaculture sustainability, reducing antibiotic dependency, and combating AMR, ultimately safeguarding public health and ecosystem resilience.

Marine Arthropods as a Source of Antimicrobial Peptides

Peptide therapeutics play a key role in the development of new medical treatments. The traditional focus on endogenous peptides has shifted from first discovering other natural sources of these molecules, to later synthesizing those with unique bioactivities. This review provides concise information concerning antimicrobial peptides derived from marine crustaceans for the development of new therapeutics. Marine arthropods do not have an adaptive immune system, and therefore, they depend on the innate immune system to eliminate pathogens. In this context, antimicrobial peptides (AMPs) with unique characteristics are a pivotal part of the defense systems of these organisms. This review covers topics such as the diversity and distribution of peptides in marine arthropods (crustacea and chelicerata), with a focus on penaeid shrimps. The following aspects are covered: the defense system; classes of AMPs; molecular characteristics of AMPs; AMP synthesis; the role of penaeidins, anti-lipopolysaccharide factors, crustins, and stylicins against microorganisms; and the use of AMPs as therapeutic drugs. This review seeks to provide a useful compilation of the most recent information regarding AMPs from marine crustaceans, and describes the future potential applications of these molecules.

Effects of the Clostridium butyricum on growth performance, antioxidant capacity, immunity and disease resistance of Litopenaeus Vannamei fed with cottonseed protein concentrate (CPC) replacement of fishmeal in diet

Clostridium butyricum (CB) is a gram-positive bacterium that secretes short-chain fatty acids such as butyric acid and so on. An 8-week feeding trial was conducted to investigate the effects of CB on the growth performance, antioxidant capacity, immunity and resistance to Vibrio parahaemolyticus in Litopenaeus Vannamei fed with cottonseed protein concentrate (CPC) replacement of fishmeal. Six iso-nitrogenous (40%) and iso-lipidic (6%) diets were formulated including a positive control group (PC, 25% fishmeal), a negative control group (NC, CPC replaced 30% of fishmeal protein), and 0.03% (C1, 3 × 10⁸ CFU/kg), 0.12% (C2, 1.2 × 10⁹ CFU/kg), 0.48% (C3, 4.8 × 10⁹ CFU/kg) and 1.92% (C4, 1.92 × 10¹⁰ CFU/kg) CB were supplemented on the negative control group (NC). After the feeding trial, the remaining shrimp in each treatment group were subjected to a challenge experiment with Vibrio parahaemolyticus. The results indicated that weight gain rate (WGR), specific growth rate (SGR) in C4 group were significantly lower than those in PC and C2 groups (P < 0.05); the feed conversion ratio (FCR) was significantly higher than that of PC and C2 groups (P < 0.05). There was no significant difference in survival rate (SR) among all groups (P > 0.05). Compared to the PC and NC groups, the total superoxide capacity, superoxide dismutase and lysozyme were significantly higher in the C4 group (P < 0.05); the glutathione peroxidase, acid phosphatase and alkaline phosphatase were significantly higher in the C3 group (P < 0.05); and the malondialdehyde was significantly lower in the C4 group (P < 0.05). The relative mRNA expressions of Toll receptor (TLR), innate immune deficiency gene (IMD), penaiedin3a (Pen3) were significantly down-regulated in the NC group than those in the PC group (P < 0.05). In addition, the relative mRNA expressions of TLR, IMD and Pen3 were significantly up-regulated in all groups supplemented with CB than those in the NC group (P < 0.05). Moreover, the cumulative mortality rate in the NC group was not significantly different from the PC group (P > 0.05) and was significantly higher than those in the C3 and C4 groups (P < 0.05). In conclusion, the CB supplementation on the basis of CPC replacement of 30% fishmeal protein enhanced significantly the antioxidant capacity, immunity and disease resistance of shrimp and improved its growth performance. Therefore, considering the factors of the growth, immunity and disease resistance, the CB supplementation of 0.12%-0.48% (1.2 × 10⁹ CFU/kg-4.8 × 10⁹ CFU/kg) was recommended in the diet of L. vannamei based on the results of this experiment.

Identification and function of an Arasin-like peptide from Litopenaeus vannamei

Antimicrobial peptides (AMPs) play an important role in the host defense system of shrimps. In this study, an Arasin-like peptide, named as LvArasin-like, was identified from the hemocytes of the pacific white shrimp, Litopenaeus vannamei. The complete open reading frame (ORF) of LvArasin-like was 213 bp, encoding 70 amino acid residues with a predicted molecular mass of 5.68 kDa and a theoretical isoelectric point (pI) of 6.73. The predicted peptide consisted of a signal peptide, an N-terminal Pro/Arg-rich domain, and a C-terminal cysteine-rich domain. LvArasin-like expression was most abundant in the gills and was up-regulated in hemocytes after LPS or Poly I:C injection as well as challenges by Vibrio parahaemolyticus or Staphylococcus aureus infection. In the heterologous expression system, LvArasin-like protein (rLvArasin-like) was recombinantly expressed in the forms of a dimer or both a monomer and dimer. The rLvArasin-like could directly bind to gram-positive and gram-negative bacteria and exhibited broad-spectrum antimicrobial activity towards them, with 50 % of minimal inhibitory concentrations (MIC50) of 6.25-50 μM. Moreover, dsRNA-mediated knockdown of LvArasin-like enhanced the susceptibility of shrimp to V. parahaemolyticus. In addition, the transcriptional level of LvArasin-like was downregulated when silencing of the transcription factors LvDorsal and LvRelish using RNAi in vivo. All of these results suggest that LvArasin-like is involved in host defense against bacterial infection. Therefore, it is a potential therapeutic agent for disease control in shrimp aquaculture.

BigPEN, an antimicrobial peptide of penaeidin family from shrimp Litopenaeus vannamei with membrane permeable and DNA binding activity

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LvBigPEN, a member of penaeidins from L. vannamei, was regulated by host AP-1 signaling pathway.

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LvBigPEN could bind to both Gram-negative bacteria and Gram-positive bacteria.

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LvBigPEN could destroy bacterial cells and bind to DNA.

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LvBigPEN played an important role in defense against V. parahaemolyticus infection.

Penaeidins are members of an antimicrobial peptide (AMP) family that have broad anti-microbial activities only found in penaeid shrimps. The LvBigPEN, a member of penaeidins from shrimp Litopenaeus vannamei, has showed antiviral activity against white spot syndrome virus (WSSV) in our previous report. However, whether LvBigPEN possesses potential anti-bacterial activities is still unknown. Herein, we found that the LvBigPEN played an important role in restricting the infection of Vibrio parahaemolyticus, a natural and Gram-negative bacteria pathogen in shrimp. The transcription of LvBigPEN was strongly induced after V. parahaemolyticus challenge. RNA interference (RNAi) mediated knockdown of LvBigPEN showed that LvBigPEN had a potential antibacterial function against V. parahaemolyticus. Microorganism binding assays indicated that rLvBigPEN could bind to both Gram-negative bacteria and Gram-positive bacteria. Transmission electron microscopy (TEM) analysis showed its ability to destroy bacterial cells in vitro. Besides, in a gel retardation assay, rLvBigPEN could bind to plasmid DNA and bacteria (V. parahaemolyticus) genomic DNA in a concentration-dependent manner. Moreover, the AP-1 pathway could participate in the transcription of LvBigPEN by the dual luciferase reporter assays. Taken together, these results suggested that LvBigPEN possessed the antibacterial activity against V. parahaemolyticus and may be alternative agents for the prevention and treatment of diseases caused by V. parahaemolyticus.

The influence of surface proteins on the probiotic effects of Lactobacillus pentosus HC-2 in the Litopenaeus vannamei hepatopancreas

Our previous work showed that Lactobacillus pentosus HC-2 has high antibacterial and adhesion activity, and as a probiotic could improve the nutrients and immunomodulatory effects in the Litopenaeus vannamei farming. In order to further investigate the influence of HC-2 surface protein on its probiotic effects, the immune and digestion related genes expression and enzymes activities, the colonization numbers of HC-2, and the histologic characteristics were analysis in shrimp hepatopancreas after feeding either the intact surface proteins, the probiotic treated with lithium chloride (LiCl) to remove noncovalently bound surface proteins or no probiotic for four weeks. The results showed that the immune genes expression of lysozyme, proPO, LGBP, Penaeidins-3α, crustin and C-type lectin, the immune enzymes activities of superoxide dismutase, catalase and Alkaline phosphatase, and the digestion enzymes of Trypsin, Lipase and α-Amylase were significantly higher in hepatopancreas of shrimp fed with intact HC-2 than that in shrimp fed with base diet or striped surface proteins HC-2 post feeding and challenge. In addition, the shrimp fed with intact HC-2 leads to the bacteria cells adhesion to hepatopancreas was significantly higher than that in shrimp fed with no surface proteins HC-2. Furthermore, the tissue damages of hepatopancreas caused by pathogenic vibrio were obviously observed in shrimp fed with base diet or no surface proteins HC-2, but no signs of damages were found in shrimp fed with intact HC-2. These results demonstrate that surface proteins are important components for HC-2 to execute probiotic effect that improve hepatopancreas immune response and nutrition digestion to protect shrimp against pathogen damage.

The Two NF-κB Pathways Regulating Bacterial and WSSV Infection of Shrimp

The outbreak of diseases ordinarily results from the disruption of the balance and harmony between hosts and pathogens. Devoid of adaptive immunity, shrimp rely largely on the innate immune system to protect themselves from pathogenic infection. Two nuclear factor-κB (NF-κB) pathways, the Toll and immune deficiency (IMD) pathways, are generally regarded as the major regulators of the immune response in shrimp, which have been extensively studied over the years. Bacterial infection can be recognized by Toll and IMD pathways, which activate two NF-κB transcription factors, Dorsal and Relish, respectively, to eventually lead to boosting the expression of various antimicrobial peptides (AMPs). In response to white-spot-syndrome-virus (WSSV) infection, these two pathways appear to be subverted and hijacked to favor viral survival. In this review, the recent progress in elucidating microbial recognition, signal transduction, and effector regulation within both shrimp Toll and IMD pathways will be discussed. We will also highlight and discuss the similarities and differences between shrimps and their Drosophila or mammalian counterparts. Understanding the interplay between pathogens and shrimp NF-κB pathways may provide new opportunities for disease-prevention strategies in the future.

Identification and function of penaeidin 3 and penaeidin 5 in Fenneropenaeus merguiensis

Antimicrobial peptides (AMPs) participate in immune defenses of invertebrate, vertebrate and plant species. As a kind of AMPs, penaeidins play important roles in innate immunity of shrimp. In this study, two penaeidin homologues termed FmPEN3 and FmPEN5 were cloned and identified from Fenneropenaeus merguiensis for the first time. The complete open reading frames (ORFs) of FmPEN3 and FmPEN5 were 216 bp and 240 bp, encoding 71 and 79 amino acids, respectively. Both FmPEN3 and FmPEN5 contain an N-terminal proline-rich domain (PRD) and a C-terminal cysteine-rich domain (CRD). The genome structure of FmPEN3 and FmPEN5 genes both consist of 2 exons and 1 intron. qPCR analysis showed that FmPEN3 was constitutively expressed but FmPEN5 transcripts were found only in hemocytes, gills, epidermis, nerve and pyloric cecum. The FmPEN3 and FmPEN5 expression were responsive to Vibrio parahaemolyticus and Micrococcus lysodeikticus infection and their transcription levels were downregulated by RNAi silencing of the transcription factors FmDorsal and FmRelish. In addition, recombinant proteins of FmPEN3 (rFmPEN3) and FmPEN5 (rFmPEN5) were successfully expressed in E. coli. The antibacterial assays revealed that rFmPEN3 and rFmPEN5 could inhibit the growth of M. lysodeikticus but only rFmPEN5 could inhibit the growth of V. parahaemolyticus in vitro. In summary, the results presented in this study indicated the functions of FmPEN3 and FmPEN5 played in anti-bacterial immunity of F. merguiensis, providing some insights into the function of AMPs in shrimp.

SpCrus3 and SpCrus4 share high similarity in mud crab (Scylla paramamosain) exhibiting different antibacterial activities

Type I crustins are crucial effectors of crustacean immune system. Various type I crustins with high sequence diversity possess different antimicrobial activities. To date, the mechanism on how the sequence diversity of type I crustins affects their antimicrobial activities is largely unclear, and how different crustins function together against bacterial invasion still remains unknown. In this study, we identified two novel type I crustins, namely, SpCrus3 and SpCrus4, from an economically important crab, Scylla paramamosain. Either SpCrus3 or SpCrus4 was highly expressed in gill. After challenges with Vibrio parahemolyticus or Staphylococcus aureus, SpCrus4 was up-regulated, whereas SpCrus3 was down-regulated. No significant expression change of SpCrus3 and SpCrus4 was observed after white spot syndrome virus injection, suggesting that these two genes may not participate in the antiviral immune responses. SpCrus3 and SpCrus4 had the common 5' terminus and high similarity of 66.06%, but SpCrus4 exhibited stronger antimicrobial activity than that of SpCrus3. Microorganism-binding assay results revealed that both SpCrus3 and SpCrus4 exhibited binding ability to all tested microorganisms. Furthermore, the polysaccharide-binding assay showed that these two proteins exhibited strong binding activity to bacterial polysaccharides, such as lipopolysaccharide (LPS), lipoteichoic acid (LTA), and peptidoglycan (PGN). SpCrus3 and SpCrus4 exhibited stronger binding activity to LPS or LTA than to PGN. Moreover, SpCrus4 showed stronger binding activity to LTA than that of SpCrus3, which may be responsible for the significantly distinct antimicrobial activity between these two proteins. In addition, SpCrus4 displayed stronger agglutination activity against several kinds of microorganisms than that of SpCrus3. This increased agglutination activity may also contribute to the strong antibacterial activity of SpCrus4. On the basis of all these results, a possible antibacterial mode exerted by SpCrus3 and SpCrus4 was proposed as follows. SpCrus3 was highly expressed in normal crabs to maintain low-level antibacterial activity without bacterial challenges. When crabs were challenged with bacteria, large amount of SpCrus4 was generated to exhibit strong antibacterial activity against bacterial invasion. This study provides new insights to understand the antibacterial functions and mechanisms of type I crustins.

Shrimp humoral responses against pathogens: antimicrobial peptides and melanization

Diseases have caused tremendous economic losses and become the major problem threatening the sustainable development of shrimp aquaculture. The knowledge of host defense mechanisms against invading pathogens is essential for the implementation of efficient strategies to prevent disease outbreaks. Like other invertebrates, shrimp rely on the innate immune system to defend themselves against a range of microbes by recognizing and destroying them through cellular and humoral immune responses. Detection of microbial pathogens triggers the signal transduction pathways including the NF-κB signaling, Toll and Imd pathways, resulting in the activation of genes involved in host defense responses. In this review, we update the discovery of components of the Toll and Imd pathways in shrimp and their participation in the regulation of shrimp antimicrobial peptide (AMP) synthesis. We also focus on a recent progress on the two most powerful and the best-studied shrimp humoral responses: AMPs and melanization. Shrimp AMPs are mainly cationic peptides with sequence diversity which endues them the broad range of activities against microorganisms. Melanization, regulated by the prophenoloxidase activating cascade, also plays a crucial role in killing and sequestration of invading pathogens. The progress and emerging research on mechanisms and functional characterization of components of these two indispensable humoral responses in shrimp immunity are summarized and discussed. Interestingly, the pattern recognition protein (PRP) crosstalk is evidenced between the proPO activating cascade and the AMP synthesis pathways in shrimp, which enables the innate immune system to build up efficient immune responses.

Antimicrobial peptides in marine invertebrate health and disease

Aquaculture contributes more than one-third of the animal protein from marine sources worldwide. A significant proportion of aquaculture products are derived from marine protostomes that are commonly referred to as 'marine invertebrates'. Among them, penaeid shrimp (Ecdysozosoa, Arthropoda) and bivalve molluscs (Lophotrochozoa, Mollusca) are economically important. Mass rearing of arthropods and molluscs causes problems with pathogens in aquatic ecosystems that are exploited by humans. Remarkably, species of corals (Cnidaria) living in non-exploited ecosystems also suffer from devastating infectious diseases that display intriguing similarities with those affecting farmed animals. Infectious diseases affecting wild and farmed animals that are present in marine environments are predicted to increase in the future. This paper summarizes the role of the main pathogens and their interaction with host immunity, with a specific focus on antimicrobial peptides (AMPs) and pathogen resistance against AMPs. We provide a detailed review of penaeid shrimp AMPs and their role at the interface between the host and its resident/pathogenic microbiota. We also briefly describe the relevance of marine invertebrate AMPs in an applied context.This article is part of the themed issue 'Evolutionary ecology of arthropod antimicrobial peptides'.

A new subfamily of penaeidin with an additional serine-rich region from kuruma shrimp (Marsupenaeus japonicus) contributes to antimicrobial and phagocytic activities

Penaeidins are an important family of antimicrobial peptides (AMPs) in penaeid shrimp. To date, five groups of penaeidins have been identified in penaeid shrimp. All are composed of a proline-rich N-terminus and a C-terminus containing six cysteine residues engaged in three disulfide bridges. In this study, a new type of penaeidin from Marsupenaeus japonicus was identified. The full-length penaeidin contains a unique serine-rich region and a penaeidin domain, which consists of a proline-rich region and a cysteine-rich region. Here, we classify all penaeidins into two subfamilies. All reported penaeidins are in subfamily I, and the new penaeidin identified in M. japonicus is designated as Penaeidin subfamily II (MjPen-II). MjPen-II was expressed in hemocytes, heart, hepatopancreas, gills, stomach and intestine, and was upregulated after bacterial challenge. A liquid bacteriostatic assay showed that MjPen-II had antibacterial activity to some Gram-positive and Gram-negative bacteria. MjPen-II could bind to bacteria by binding to polysaccharides on the surface of bacteria, thus promoting bacterial agglutination. The serine-rich region enhanced the agglutination activity of MjPen-II. The proline-rich domain had a stronger bacterial-binding activity and polysaccharide-binding activity than the cysteine-rich domain. MjPen-II was also found to be involved in the phagocytosis of bacteria and efficiently improved the phagocytosis rate. Therefore, MjPen-II eliminates bacteria through direct bacterial inhibition as well as by promoting phagocytosis in shrimp.

Four crustins involved in antibacterial responses in Marsupenaeus japonicus

Crustins are a family of cationic, cysteine-rich antimicrobial peptides with a whey acidic protein (WAP) domain in the C-terminal. They have diverse functions in antimicrobial immune responses. Four groups of crustins (crustins I, II, III, and IV) have been identified in crustaceans, but type I crustins have not been reported in penaeid shrimp until now. In this study, we identified four crustins in kuruma shrimp Marsupenaeus japonicus, and named them MjCrus I-2, 3, 4 and 5. These four crustins belong to type I crustins, which contain a signal peptide, cysteine-rich region at the N-terminus, and WAP domain at the C-terminus. Tissue distribution demonstrated that MjCrus I-2, 3 and 5 had high expression levels in hemocytes, gills and stomach. whereas MjCrus I-4 was distributed in all tissues detected. MjCrus I-2 to 5 showed different expression patterns in different tissues after Gram-positive bacterial (Staphylococcus aureus), Gram-negative bacterial (Vibrio anguillarum), and white spot syndrome virus (WSSV) challenge. The expression of MjCrus I-2 to 5 was upregulated by bacterial or WSSV challenge. The three crustins were recombinantly expressed in Escherichia coli, and the purified proteins showed few antimicrobial activities. Three MjCrus Is could bind to different bacteria. MjCrus I-2 and 3 showed different inhibitory abilities to secreted bacterial proteases. MjCrus I-4 could not inhibit bacterial proteases. After knockdown of MjCrus I-3, the bacterial scavenging ability to V. anguillarum was impaired. These results suggested that type I crustins played an important role in the innate immunity of shrimp.

Role of evolutionarily conserved signaling intermediate in Toll pathways (ECSIT) in the antibacterial immunity of Marsupenaeus japonicus

The Toll/Toll-like receptor (TLR) signaling pathway has an important role in the innate immunity of animals. Evolutionarily conserved signaling intermediate in Toll pathways (ECSIT) is a protein that functions as an adaptor protein for the Toll/TLR and bone morphogenetic protein signaling pathways. ECSIT is also a key component in the macrophage bactericidal activity of mammals. However, the function of ECSIT in crustaceans remains unclear. In this study, we cloned and identified a functional ECSIT homologue, MjECSIT 1, from kuruma shrimp Marsupenaeus japonicus. The complementary DNA of MjEcsit 1 is 1442 base pairs long, with an open reading frame of 1221 base pairs that encodes a 407-residue polypeptide. Transcripts of MjEcsit 1 are detected in hemocytes, gills, hepatopancreas, stomach, heart, intestines, testes, and ovaries. Such transcripts are upregulated by Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Vibrio anguillarum) injections. The knockdown of MjEcsit 1 by double-stranded RNA injection increases the sensitivity of M. japonicus to S. aureus challenge and weakens the bacterial clearance ability of M. japonicus in vivo. In addition, suppressing MjEcsit 1 restrains the upregulation of two anti-lipopolysaccharide factors by S. aureus injection. The results indicate that MjECSIT 1 is important in the antibacterial immunity of M. japonicus.

Functional analysis of Fenneropenaeus chinensis anti-lipopolysaccharide factor promoter regulated by lipopolysaccharide and (1,3)-β-D-glucan

Current knowledge on cis-regulatory elements of immune genes of shrimp is poor. In this study, the genomic sequence of the Fenneropenaeus chinensis anti-lipopolysaccharide factor (ALFFc) gene was obtained by using PCR and genome walking techniques, and the promoter was identified. The ALFFc gene contained three exons interrupted by two introns. Immune-related transcription factor binding sites recognized by nuclear factor-kappa B, octamer binding protein 1, GATA binding factor 1 and specificity protein 1 were identified in the regin from +1 to -702. The activity of ALFFc promoter was analyzed in insect sf9 cell lines. The putative promoter sequence of pALF-702 drive the expression of reporter EGFP gene successfully by adding lipopolysaccharide or (1,3)-β-D-glucan, but the shorter promoter sequence pALF-318 is only by (1,3)-β-D-glucan. The results pointed out that these transcription elements might contribute to the differences in promoter of ALFFc. Our results would provide supports for future studies to identify the functional transcription elements in the ALF promoter and to expand our knowledge on regulation of innate immune genes in Chinese shrimp.

Characterization of an immune deficiency homolog (IMD) in shrimp (Fenneropenaeus chinensis) and crayfish (Procambarus clarkii)

The immune deficiency (IMD) signal pathway mediates immunity against Gram-negative bacteria in Drosophila. Recent studies show that the IMD pathway also involves in antiviral innate immune responses. The functions of the pathway in crustacean immunity are largely unknown. In this paper, two IMDs (FcIMD and PcIMD), one of the key elements of the IMD pathway, were identified from Chinese white shrimp Fenneropenaeus chinensis and red swamp crayfish Procambarus clarkii. Both proteins have a death domain located at the C-terminal. FcIMD was mainly expressed in the gills and stomach and PcIMD was mainly detected in the heart, hepatopancreas, and stomach. FcIMD peaked in hemocytes at 12 h after white spot syndrome virus (WSSV) challenge and it peaked in the gills at 6 h after WSSV challenge, but it was decreased at 2 h and kept the low level to 24 h in hemocytes and no obviously change in gill after Vibrio anguillarum challenge. PcIMD first decreased in hemocytes at 2 h and peaked at 12 h in hemocytes after V. anguillarum challenge. It was also upregulated in gill after bacterial challenge, peaked at 2 h, and decreased at 6 h, and then gradually increased at 12-24 h. PcIMD has no significant change in hemocytes and gill after WSSV challenge. Western blot analysis detected FcIMD protein in all tissues, and immunocytochemical analysis localized FcIMD in the cytoplasm of hemocytes. RNA interference analysis showed that the IMD pathway was involved in regulating the expression of three kinds AMP genes, including crustins, anti-lipopolysaccharide factors and lysozymes, in shrimp and crayfish. They are Cru 1, Cru 2, ALF 1, ALF 2 and Lys 1 in crayfish, and Cru1, Cru 3, ALF 6, ALF 8, and Lys2 in shrimp. These results suggest that although IMD distribution and expression patterns have some differences, the IMD pathway may have conserved function for AMP regulation in shrimp and crayfish immunity against Gram-negative bacteria.

A single whey acidic protein domain containing protein (SWD) inhibits bacteria invasion and dissemination in shrimp Marsupenaeus japonicus

The single whey acidic protein (WAP) domain containing proteins (SWDs) in crustacean belong to type III crustins and have antiprotease activities and/or antimicrobial activities. Their functions in vivo in crustacean immunity need to be clarify. In this study, a new single WAP domain containing protein (SWD) was obtained from Marsupenaeus japonicus, designated as MjSWD. The full-length cDNA of MjSWD was 522 bp.The open reading frame of MjSWD encoded a protein of 79 amino acids, with a 24 amino acid signal peptide and a WAP domain. Tissue distribution analysis revealed that MjSWD transcripts were generally expressed in all the tested tissues, including hemocytes, heart, hepatopancreas, gill, stomach and intestine. The time course expression of MjSWD was analyzed by quantitative real time PCR, and the results exhibited that MjSWD was upregulated after bacteria (Vibrio anguillarum, Staphylococcus aureus) and white spot syndrome virus (WSSV) challenge in gills and stomach of the shrimp. The purified recombinant protein of MjSWD could bind to several Gram-negative and Gram-positive bacteria though binding to microbial polysaccharides (peptidoglycan). MjSWD could inhibit the activity of Subtilisin A and Proteinase K and bacteria-secreted proteases. The results of natural infection with MjSWD incubated bacteria showed that the inhibition of MjSWD against bacterial secreted proteases was contributed to inhibiting bacteria invasion and dissemination in the shrimp. The MjSWD is, thus, involved in the shrimp antibacterial innate immunity.

Procambarin: a glycine-rich peptide found in the haemocytes of red swamp crayfish Procambarus clarkii and its response to white spot syndrome virus challenge

We cloned a novel glycine-rich peptide, procambarin, from the haemocytes of unchallenged crayfish Procambarus clarkii. The mature peptide (155 residues) has a13.44 KDa molecular mass with a theoretical pI about 12.12. It is characterized by a high level of glycine (57.42%) and a threefold repeated motif GLKPNVGGGGGFGGG. Generally, it belongs to cationic glycine-rich peptide. The transcripts of this peptide were detected in many tissues. The haemocytes showed the highest expression of glycine-rich peptide mRNA, followed by the ovaries, antennal gland and intestine. The gill, hepatopancreas and heart showed little expression of this peptide and no expression was detected in the musculature. There is no intron in the ORF of it. The fluctuation of mRNA expression level of procambarin after WSSV challenge indicates that this peptide participates in the antiviral immune reaction.

Discovery of immune molecules and their crucial functions in shrimp immunity

Several immune-related molecules in penaeid shrimps have been discovered, most of these via the analysis of expressed sequence tag libraries, microarray studies and proteomic approaches. These immune molecules include antimicrobial peptides, serine proteinases and inhibitors, phenoloxidases, oxidative enzymes, clottable protein, pattern recognition proteins, lectins, Toll receptors, and other humoral factors that might participate in the innate immune system of shrimps. These molecules have mainly been found in the hemolymph and hemocytes, which are the main sites where immune reactions take place, while some are found in other immune organs/tissues, such as the lymphoid organs, gills and intestines. Although the participation of some of these immune molecules in the shrimp innate immune defense against invading pathogens has been demonstrated, the functions of many molecules remain unclear. This review summarizes the current status of our knowledge concerning the discovery and functional characterization of the immune molecules in penaeid shrimps.

Recent advances in researches on the innate immunity of shrimp in China

The annual production of shrimp culture in mainland of China has been over one million tons for several years. The major cultivated penaeidae species are Litopenaeus vannamei, Fenneropenaeus chinensis, Penaeus monodon and Marsupenaeus japonicus. Due to the importance of shrimp aquaculture in China, researchers have paid more attention to the molecular mechanism of shrimp disease occurrence and tried to develop an efficient control strategy for disease. This paper summarizes the research progress related to innate immunity of penaeid shrimp made in the last decade in Mainland China. Several pattern recognition receptors, such as lectin, toll, lipopolysaccharide and β-1,3-glucan binding protein (LGBP) and tetraspanin were identified. The major signal transduction pathways, including Toll pathway, IMD pathway, which might be involved in the immune response of shrimp, were focused on and most of the components in Toll pathway were identified. Also, cellular immune responses such as phagocytosis and apoptosis were regarded playing very important roles in anti-WSSV infection to shrimp. The molecules involved in the maintenance of the immune homeostasis of shrimp and the progress on molecular structure and pathogenic mechanism of WSSV were summarized. Therefore, the brief outline about the immune system of shrimp is drawn based on the recent data which will help us to understand the immune responses of shrimp to different pathogens.

Molecular characterization of three crustin genes in the morotoge shrimp, Pandalopsis japonica

Crustins are among the most important antimicrobial peptides (AMPs) found in decapod crustaceans. They are small cationic AMPs (5-7 kDa) characterized by a proline-rich amino-terminal domain and a cysteine-rich carboxyl-terminal domain. Here, the first 3 crustin-like cDNAs (Pj-crus Ia, Ib, and II) were identified from the morotoge shrimp, Pandalopsis japonica. The full-length cDNAs of Pj-crus Ia, Ib, and II consisted of 1135, 580, and 700 nucleotides and encoded putative proteins containing 109, 119, and 186 amino acids residues, respectively. All 3 identified Pj-crus sequences exhibited the conserved domain organization for crustins, including a signal sequence, a cysteine-containing region, a glycine-rich region, and a whey-acidic protein (WAP) domain. Amino acid sequence comparisons and phylogenetic analysis revealed that the Pj-crus Ia and Ib belong to type I crustins (e.g., carcinin), which have been mostly identified from Brachyura and Astacidea, whereas Pj-crus II was classified as belonging to the type II crustins, which are mainly found in Dendrobranchiata. An analysis of the organization of these 3 Pj-crus genes revealed that the splicing site within the WAP domain may be an important key for classifying types I and II crustin family members. The tissue distribution profile results showed that the Pj-crus I genes were expressed in a tissue-specific manner but that the Pj-crus II gene was expressed ubiquitously, suggesting that these crustins may play different roles in various tissues or under different physiological conditions. The bacterial challenge results suggested that the Pj-crus genes may be transcriptionally influenced by different bacterial types. This comparative study of various crustin family members will help extend the knowledge on the crustacean innate immune response, which will provide important basic information for controlling shrimp immunity against various pathogens.

Six defensins from the triangle-shell pearl mussel Hyriopsis cumingii

Antimicrobial peptides (AMPs) are the first line of defense of invertebrates against invading pathogens. Defensins, unique AMPs, have a cysteine-stabilized α-helix and β-sheet (CSαβ) motif. In invertebrates, defensins have been reported in arthropods and mussels. Recently, six defensins were identified from Hyriopsis cumingii for the first time, and were designated as HcDef1, HcDef2, HcDef3, HcDef4, HcDef5, and HcDef6. HcDef1 and HcDef2 encode a protein containing 61 and 60 amino acids, respectively. HcDef3, HcDef4, and HcDef6 have 65 amino acids each. HcDef5 is longer than the other five defensins, comprising 83 amino acids. HcDef3 and HcDef4 have three pairs of disulfide bonds. HcDef1, HcDef5, and HcDef6 are exceptions; each has four pairs of disulfide bonds. Evolutionary analysis revealed that only purifying selection and no positive selection could be detected in defensin genes; purifying selection might be the major evolutionary driving force in the evolution of defensin genes. The present study reveals for the first time that the defensins from H. cumingii are diverse and phylogenetic analysis showed that these 6 defensins from H. cumingii were clustered into one group. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis showed that HcDef1-HcDef4 could be detected in the hepatopancreas and gills whereas HcDef5-HcDef6 could only be detected in gills. In addition, the expression levels of HcDef2, HcDef3, and HcDef5 in H. cumingii with pearls were higher than that in H. cumingii without pearls. Quantitative RT-PCR analysis showed that HcDef1, HcDef2, HcDef3, and HcDef5 were downregulated by Vibrio anguillarum challenge whereas HcDef4 and HcDef6 were upregulated under Vibrio challenge. Our results suggest the roles of defensins in the innate immunity of H. cumingii.

Expression of a novel antimicrobial peptide Penaeidin4-1 in creeping bentgrass (Agrostis stolonifera L.) enhances plant fungal disease resistance

Background

Turfgrass species are agriculturally and economically important perennial crops. Turfgrass species are highly susceptible to a wide range of fungal pathogens. Dollar spot and brown patch, two important diseases caused by fungal pathogens Sclerotinia homoecarpa and Rhizoctonia solani, respectively, are among the most severe turfgrass diseases. Currently, turf fungal disease control mainly relies on fungicide treatments, which raises many concerns for human health and the environment. Antimicrobial peptides found in various organisms play an important role in innate immune response.

Methodology/Principal Findings

The antimicrobial peptide - Penaeidin4-1 (Pen4-1) from the shrimp, Litopenaeus setiferus has been reported to possess in vitro antifungal and antibacterial activities against various economically important fungal and bacterial pathogens. In this study, we have studied the feasibility of using this novel peptide for engineering enhanced disease resistance into creeping bentgrass plants (Agrostis stolonifera L., cv. Penn A-4). Two DNA constructs were prepared containing either the coding sequence of a single peptide, Pen4-1 or the DNA sequence coding for the transit signal peptide of the secreted tobacco AP24 protein translationally fused to the Pen4-1 coding sequence. A maize ubiquitin promoter was used in both constructs to drive gene expression. Transgenic turfgrass plants containing different DNA constructs were generated by Agrobacterium-mediated transformation and analyzed for transgene insertion and expression. In replicated in vitro and in vivo experiments under controlled environments, transgenic plants exhibited significantly enhanced resistance to dollar spot and brown patch, the two major fungal diseases in turfgrass. The targeting of Pen4-1 to endoplasmic reticulum by the transit peptide of AP24 protein did not significantly impact disease resistance in transgenic plants.

Conclusion/Significance

Our results demonstrate the effectiveness of Pen4-1 in a perennial species against fungal pathogens and suggest a potential strategy for engineering broad-spectrum fungal disease resistance in crop species.

Invertebrate immune diversity

The arms race between hosts and pathogens (and other non-self) drives the molecular diversification of immune response genes in the host. Over long periods of evolutionary time, many different defense strategies have been employed by a wide variety of invertebrates. We review here penaeidins and crustins in crustaceans, the allorecognition system encoded by fuhc, fester and Uncle fester in a colonial tunicate, Dscam and PGRPs in arthropods, FREPs in snails, VCBPs in protochordates, and the Sp185/333 system in the purple sea urchin. Comparisons among immune systems, including those reviewed here have not identified an immune specific regulatory "genetic toolkit", however, repeatedly identified sequences (or "building materials" on which the tools act) are present in a broad range of immune systems. These include a Toll/TLR system, a primitive complement system, an LPS binding protein, and a RAG core/Transib element. Repeatedly identified domains and motifs that function in immune proteins include NACHT, LRR, Ig, death, TIR, lectin domains, and a thioester motif. In addition, there are repeatedly identified mechanisms (or "construction methods") that generate sequence diversity in genes with immune function. These include genomic instability, duplications and/or deletions of sequences and the generation of clusters of similar genes or exons that appear as families, gene recombination, gene conversion, retrotransposition, alternative splicing, multiple alleles for single copy genes, and RNA editing. These commonly employed "materials and methods" for building and maintaining an effective immune system that might have been part of that ancestral system appear now as a fragmented and likely incomplete set, likely due to the rapid evolutionary change (or loss) of host genes that are under pressure to keep pace with pathogen diversity.

Cationic antimicrobial peptides in penaeid shrimp

Penaeid shrimp aquaculture has been consistently affected worldwide by devastating diseases that cause a severe loss in production. To fight a variety of harmful microbes in the surrounding environment, particularly at high densities (of which intensive farming represents an extreme example), shrimps have evolved and use a diverse array of antimicrobial peptides (AMPs) as part of an important first-line response of the host defense system. Cationic AMPs in penaeid shrimps composed of penaeidins, crustins, and anti-lipopolysaccharide factors are comprised of multiple classes or isoforms and possess antibacterial and antifungal activities against different strains of bacteria and fungi. Shrimp AMPs are primarily expressed in circulating hemocytes, which is the main site of the immune response, and hemocytes expressing AMPs probably migrate to infection sites to fight against pathogen invasion. Indeed, most AMPs are produced as early as the nauplii developmental stage to protect shrimp larvae from infections. In this review, we discuss the sequence diversity, expression, gene structure, and antimicrobial activities of cationic AMPs in penaeid shrimps. The information available on antimicrobial activities indicates that these shrimp AMPs have potential therapeutic applications in the control of disease problems in aquaculture.

The possible role of penaeidin5 from the black tiger shrimp, Penaeus monodon, in protection against viral infection

Penaeidin class 5 (PEN5) has so far only been reported in the Chinese shrimp, Fenneropenaeus chinensis, and the black tiger shrimp, Penaeus monodon. The PEN5 homolog from F. chinensis (FenchiPEN5) exhibits antimicrobial activities against both Gram-positive and Gram-negative bacteria as well as fungi. Here, we characterized the PEN5 gene from P. monodon (PenmonPEN5) and evaluated its potential involvement in antiviral immunity. The deduced open reading frame of PenmonPEN5 encodes for a predicted 79 amino acid peptide including a 19 amino acid signal peptide. The gene structure of PenmonPEN5 contains two exons interrupted by one intron, whilst the 5' upstream sequence contains a putative TATA box and several GATA, GATA-3, AP-1 and dorsal transcription factor binding sites. PenmonPEN5 mRNA levels in P. monodon shrimps following a systemic infection with white spot syndrome virus (WSSV) were significantly induced at 24 h post infection, but was strongly down-regulated at 48 h post injection, compared to those of the uninfected control shrimps. The suppression of PenmonPEN5 transcript levels by RNA interference mediated gene silencing led to an increased susceptibility of shrimps to WSSV infection, suggesting a possible role of PenmonPEN5 in the shrimp's antiviral immunity.

Cationic antimicrobial peptides in penaeid shrimp

Penaeid shrimp aquaculture has been consistently affected worldwide by devastating diseases that cause a severe loss in production. To fight a variety of harmful microbes in the surrounding environment, particularly at high densities (of which intensive farming represents an extreme example), shrimps have evolved and use a diverse array of antimicrobial peptides (AMPs) as part of an important first-line response of the host defense system. Cationic AMPs in penaeid shrimps composed of penaeidins, crustins, and anti-lipopolysaccharide factors are comprised of multiple classes or isoforms and possess antibacterial and antifungal activities against different strains of bacteria and fungi. Shrimp AMPs are primarily expressed in circulating hemocytes, which is the main site of the immune response, and hemocytes expressing AMPs probably migrate to infection sites to fight against pathogen invasion. Indeed, most AMPs are produced as early as the nauplii developmental stage to protect shrimp larvae from infections. In this review, we discuss the sequence diversity, expression, gene structure, and antimicrobial activities of cationic AMPs in penaeid shrimps. The information available on antimicrobial activities indicates that these shrimp AMPs have potential therapeutic applications in the control of disease problems in aquaculture.

Molecular cloning and characterization of three crustins from the Chinese white shrimp, Fenneropenaeus chinensis

Antibacterial peptides crustins are the effector molecules of innate immunity in decapods. In this study, three crustin cDNA sequences (Fc-crus 1, Fc-crus 2, and Fc-crus 3) were cloned from the Chinese white shrimp Fenneropenaeus chinensis. The full-length cDNAs of Fc-crus 2 and 3 are 473 bp and 574 bp, respectively. The deduced peptides of Fc-crus 2 and 3 contain a signal peptide and a crustin domain at the C-terminal formed by twelve conserved cysteine residues. The partial sequence of Fc-cru 1 is 575 bp long and the deduced amino acids also contain a crustin domain. The expression profiles of these three crustins were studied with RT-PCR. Fc-crus 1 and Fc-crus 2 constitutively expressed in hemocytes with high levels, and the expression level is increased in the heart, stomach, intestine and ovaries when shrimp was challenged with Vibrio anguillarum, The expression of Fc-crus 1 and Fc-crus 2 was detected in each developmental stage. Fc-crus 3 was constitutively expressed in the ovaries and induced as an expression in the stomach. Unlike Fc-crus 1 and Fc-crus 2, the mRNA of Fc-crus 3 was not detected in the developmental stages extending from nauplii and mysis to post-larvae. The recombinant proteins containing mature Fc-crus 2 and Fc-crus 3 were recombinantly expressed in Escherichia coli and respectively purified. The antibacterial assays revealed that the recombinant mFc-crus could inhibit the growth of Gram-positive bacteria in vitro.

Identification of a novel relish homolog in Chinese shrimp Fenneropenaeus chinensis and its function in regulating the transcription of antimicrobial peptides

Penaeid shrimp, as an invertebrate, relies on the innate immunity to oppose the microbial invaders. Antimicrobial peptides (AMP) are an integral component of the innate immune system in most organisms and function as an early first line of defense against pathogens, but the knowledge about the pathways to regulate the shrimp AMP gene expression is still absent up to date. In the current study, a Relish homolog (FcRelish) was cloned from Chinese shrimp Fenneropenaeus chinensis. The full length cDNA of FcRelish consists of 2157 bp, including 1512 bp open reading frame, encoding 504 amino acids. The predicted molecular weight of FcRelish is 57 kDa, and the theoretical PI is 7.00. Spatial expression profiles showed that FcRelish had the highest expression levels in the hemocytes and lymphoid organ. Both Vibrio anguillarium and Micrococcus lysodeikticus stimulation to shrimp can affect the transcription profile of FcRelish. Silencing of FcRelish through DsRNA interference can greatly change the transcription profile of AMP. Therefore, we suggest that FcRelish identified in the present study is closely related to the transcription of AMP, and then we inferred that Imd pathway might exist in shrimp.

Cloning of penaeidin gene promoter in tiger shrimp (Penaeus monodon)

Penaeidins belong to a family of antimicrobial peptides that are expressed in the hemocytes of penaeid shrimps. Using an extender PCR method and a nested PCR, we cloned two types of genomic fragment flanking the 5' end of penaeidin gene in tiger shrimp (Penaeus monodon): Type536 and Type411 sequences. Both fragments contained TATA box, GATA, dorsal and AP-1 motifs and were ligated to an expression vector with a luciferase reporter gene. The constructs were then delivered into Drosophila S2 cell line. The promoter functions of the two fragments were determined using a luciferase expression assay. The study demonstrated that Type411 sequence performed higher transcriptional activity than Type536. Alignment of the upstream sequences of penaeidin genes in P. monodon and Litopenaeus vannamei showed that the promoter regions were obviously more diverse than the 5'UTRs. Phylogenetic analysis indicated the presence of two types of promoters that are not species-specific in the two shrimps.

A relationship between antimicrobial peptide gene expression and capacity of a selected shrimp line to survive a Vibrio infection

Understanding of antimicrobial defence mechanisms of penaeid shrimp should help in the design of efficient strategies for the management and disease control in aquaculture. In this study, we have specifically analysed the expression in circulating hemocytes of antimicrobial peptides (AMPs) encoding genes, such as PEN2 and PEN3, ALF, crustin, lysozyme and a putative cysteine-rich peptide. We evidenced a relationship between the level of expression of some AMPs and the successful response of the shrimp, Litopenaeus stylirostris, to circumvent a pathogenic Vibrio penaeicida infection. Additionally, significant differences in some AMP transcript amounts are evidenced between control, non-selected shrimp line and the third generation breeding of shrimp selected for their survival to natural V. penaeicida infections. On the basis of these results, it will now be of great interest to determine if these AMPs are directly involved in the resistance of shrimp to infection or if they only reflect other acquired defence mechanisms which can confer a resistance.

A novel antimicrobial peptide from amphibian skin secretions of Odorrana grahami

A novel antimicrobial peptide named odorranain-NR was identified from skin secretions of the diskless odorous frog, Odorrana grahami. It is composed of 23 amino acids with an amino acid sequence of GLLSGILGAGKHIVCGLTGCAKA. Odorranain-NR was classified into a novel family of antimicrobial peptide although it shared similarity with amphibian antimicrobial peptide family of nigrocin. Odorranain-NR has an unusual intramolecular disulfide-bridged hexapeptide segment that is different from the intramolecular disulfide-bridged heptapeptide segment at the C-terminal end of nigrocins. Furthermore, the -AKA fragment at the C-terminal of odorranain-NR is also different from nigrocins. Three different cDNAs encoding two odorranain-NR precursors and only one mature odorranain-NR was cloned from the cDNA library of the skin of O. grahami. This peptide showed antimicrobial activities against tested microorganisms except Escherichia coli (ATCC25922). Its antimicrobial mechanisms were investigated by transmission electron microcopy. Odorranain-NR exerted its antimicrobial functions by various means depending on different microorganisms.

Molecular cloning, genomic organization and recombinant expression of a crustin-like antimicrobial peptide from black tiger shrimp Penaeus monodon

A novel crustin-like antimicrobial peptide (Crus-likePm) was identified from haemocytes of Penaeus monodon. The deduced amino acid sequence of a Crus-likePm consists of 124 amino acid residues of the mature peptide and a signal peptide of 17 amino acid residues. The mature peptide contains a glycine-rich domain at the N-terminus and 12 conserved cysteine residues containing a single WAP domain at the C-terminus. Phylogenetic tree and sequence comparison clearly confirmed a distinct between a Crus-likePm and other shrimp crustins. Genomic organization and upstream region of a Crus-likePm gene was investigated. The gene consisted of two exons and one intron. The 5'-flanking regions of a Crus-likePm gene contain multiple putative transcription factor binding sites. mRNA transcript of a Crus-likePm was found to be abundantly expressed in haemocyte and highly up-regulated after Vibrio harveyi injection. The mature Crus-likePm was cloned into the pET28b with an N-terminal hexa-histidine tag fused in-frame, and expressed in E. coli. The purified recombinant Crus-likePm showed strong antimicrobial activity against both Gram-positive and Gram-negative bacteria including V. harveyi, a major pathogenic bacteria in shrimp aquaculture.

Isolation and functional characterization of a new shrimp ovarian peritrophin with antimicrobial activity from Fenneropenaeus merguiensis

Shrimp ovarian peritrophin (SOP), a major protein in jelly layer (JL) and cortical rods (CRs), is proposed to play a role in the protection of spawned eggs. The full sequence of SOP cDNA from Fenneropenaeus merguiensis (Fm-SOP) shares approximately 50% identity with other SOP sequences and contains several putative chitin-binding or peritrophin-A domains. Interestingly, Fm-SOP contains a putative 61-amino acid propeptide located at the N-terminal end, downstream of a 19-amino acid signal peptide, which is unique among penaeid SOP sequences described so far. This 61-amino-acid sequence constitutes a putative chitin-binding domain with six conserved cysteines, and is cleaved at a dibasic recognition site for a furin (subtilisin-like endoprotease). Expression analyses indicated that Fm-SOP mRNA is abundant in early vitellogenic ovaries and scarce in late-vitellogenic ovaries. Conversely, Fm-SOP protein is the most abundant at the end of vitellogenesis. To investigate its biological function, a recombinant Fm-SOP was expressed to generate a glycosylated protein in Spodoptera frugiperda Sf9 cells (rSOP-Sf9) and a nonglycosylated protein (rSOP-Ec) in Escherichia coli. rSOP-Sf9 and rSOP-Ec were found to bind to chitin, similarly to the native protein extracted from F. merguiensis ovaries. Most interestingly, rSOP-Ec displayed a chitinase activity and efficiently inhibited the growth of Vibrio harveyi and Staphylococcus aureus, with minimum inhibitory concentrations of 2.4 and 15.7 microM, respectively. This first report shows that a major component of CR and JL is biologically active against known pathogens and predicts a significant role of JL in the protection of the spawned eggs against pathogens.

Adaptive evolution after duplication of penaeidin antimicrobial peptides

Penaeidin antimicrobial peptides in penaeid shrimps are an important component of their innate immune system that provides immunity against infection caused by several gram-positive bacteria and filamentous fungal species. Despite the knowledge on the identification and characterization of these peptides in penaeid shrimps, little is known about the evolutionary pattern of these peptides and the underlying genetic mechanisms that maintain high sequence diversities in the penaeidin gene family. Based on the phylogenetic analyses and maximum likelihood-based codon substitution analyses, here we present the convincing evidence that multiple copies of penaeidins have evolved by gene duplication, and positive Darwinian selection (adaptive evolution) is the likely cause of accelerated rate of amino acid substitutions among these duplicated genes. While the average ratio of non-synonymous to synonymous substitutions (omega) for the entire coding region of both active domains is 0.9805, few codon sites showed significantly higher omega (3.73). The likelihood ratio tests that compare models incorporating positive selection (omega>1) at certain codon sites with models not incorporating positive selection (omega<1), failed to reject (p=0) the evidence of positive Darwinian selection. The rapid adaptive evolution of this gene family might be directed by the pathogens and the faster rate of amino acid substitutions in the N-terminal proline-rich and C-terminal cysteine-rich domains could be due to their direct involvement in the protection against pathogens. When the host expose to different habitats/environment an accelerated rate of amino acid substitutions in both the active domains may also be expected.

Diversity in penaeidin antimicrobial peptide form and function

Penaeidins are a diverse family of two-domain antimicrobial peptides expressed in shrimp. Variation in penaeidin sequence results in functional diversity, which was discovered using synthetic reproductions of native penaeidins. An isoform of penaeidin class 3 from Litopenaeus setiferus (Litset Pen3-4) was synthesized using native ligation and compared directly with the synthetic penaeidin class 4 known to be expressed in the same organism. New antimicrobial activity data are included in this review that emphasize differences in effectiveness that are apparent from a direct comparison of two classes. A novel approach to intact penaeidin analysis is presented in the form of Fourier Transform Ion-Cyclotron Resonance Mass Spectrometry, which has implications for the identification of individual penaeidin isoforms without chemical modification or enzymatic cleavage. The new information included in this review helps gather the perspective on relevance of penaeidin diversity to antimicrobial function, the use of synthetic peptides as tools to evaluate specific immune functions and the application of high mass resolution, top-down sequencing methods to the intact analysis of individual penaeidin isoforms.