Prediction and characterization of a novel hemocyanin-derived antimicrobial peptide from shrimp Litopenaeus vannamei

Shrimp hemocyanin elicits a potent humoral response in mammals and is favorable to hapten conjugation

Conjugation to a carrier protein is essential to give rise to the antigenicity of hapten. Three carrier proteins e.g. KLH (Keyhole Limpet hemocyanin), BSA (bovine serum albumin), and OVA (Ovalbumin) were used mostly. KLH is advantageous to the others, majorly owing to its strong immunogenicity and limited usage in other biological assays. However, the cost of obtaining Keyhole Limpet is high and the solubility of KLH is not as well as the other carriers, especially after hapten conjugation. Here, we extracted the shrimp hemocyanin (SHC) from Litopenaeus vannamei (L. vannamei), which is a commonly sea product worldwide. The high pure SHC could be acquired by two-step purification, with a production yield of > 1 g proteins (98% pure) per 1 kg shrimp. Compared to KLH, the peptide-SHC conjugates exhibit higher solubility after hapten conjugation. Meanwhile, compared with KLH, SHC induces comparable antibody production efficiency in mammals, with or without conjugation. Furthermore, rabbit polyclonal antibodies or mouse monoclonal antibodies were generated by immunizing SHC-peptide conjugates, and the subsequent antibodies were confirmed to be used in western blot, immunofluorescence and immunohistochemistry. Therefore, we demonstrated that SHC may be used as a substitute for KLH in future antibody and vaccine development.

Antibacterial Properties of Peptide and Protein Fractions from Cornu aspersum Mucus

The discovery and investigation of new natural compounds with antimicrobial activity are new potential strategies to reduce the spread of antimicrobial resistance. The presented study reveals, for the first time, the promising antibacterial potential of two fractions from Cornu aspersum mucus with an MW < 20 kDa and an MW > 20 kDa against five bacterial pathogens-Bacillus cereus 1085, Propionibacterium acnes 1897, Salmonella enterica 8691, Enterococcus faecalis 3915, and Enterococcus faecium 8754. Using de novo sequencing, 16 novel peptides with potential antibacterial activity were identified in a fraction with an MW < 20 kDa. Some bioactive compounds in a mucus fraction with an MW > 20 kDa were determined via a proteomic analysis on 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and bioinformatics. High homology with proteins and glycoproteins was found, with potential antibacterial activity in mucus proteins named aspernin, hemocyanins, H-lectins, and L-amino acid oxidase-like protein, as well as mucins (mucin-5AC, mucin-5B, mucin-2, and mucin-17). We hypothesize that the synergy between the bioactive components determined in the composition of the fraction > 20 kDa are responsible for the high antibacterial activity against the tested pathogens in concentrations between 32 and 128 µg/mL, which is comparable to vancomycin, but without cytotoxic effects on model eukaryotic cells of Saccharomyces cerevisiae. Additionally, a positive effect, by reducing the levels of intracellular oxidative damage and increasing antioxidant capacity, on S. cerevisiae cells was found for both mucus extract fractions of C. aspersum. These findings may serve as a basis for further studies to develop a new antibacterial agent preventing the development of antibiotic resistance.

A comprehensive review on hemocyanin from marine products: Structure, functions, its implications for the food industry and beyond

Hemocyanin, an oxygen-transport protein, is widely distributed in the hemolymph of marine arthropods and mollusks, playing an important role in their physiological processes. Recently, hemocyanin has been recognized as a multifunctional glycoprotein involved in the immunological responses of aquatic invertebrates. Consequently, the link between hemocyanin functions and their potential applications has garnered increased attention. This review offers an integrated overview of hemocyanin's structure, physicochemical characteristics, and bioactivities to further promote the utilization of hemocyanin derived from marine products. Specifically, we review its implication in two aspects of food and aquaculture industries: quality and health. Hemocyanin's inducible phenoloxidase activity is thought to be an inducer of melanosis in crustaceans. New anti-melanosis agents targeted to hemocyanin need to be explored. The red-color change observed in shrimp shells is related to hemocyanin, affecting consumer preferences. Hemocyanin's adaptive modification in response to the aquatic environment is available as a biomarker. Additionally, hemocyanin is endowed with bioactivities encompassing anti-microbial, antiviral, and therapeutic activities. Hemocyanin is also a novel allergen and its allergenic features remain incompletely characterized.

Characterization of a pseudohemocyanin gene (PtPhc1) and its immunity function in response to Vibrio parahaemolyticus infection in the swimming crab Portunus trituberculatus

Pseudohemocyanin is a member of the hemocyanin superfamily, but little research is available on its function in immunology. In this study, a Portunus trituberculatus pseudohemocyanin gene, named PtPhc1, was obtained by gene cloning. The PtPhc1 cDNA was 2312 bp in length, encoding 684 amino acids while exhibiting a characteristic hemocyanin structural domain. Tissue expression analysis revealed ubiquitous expression of PtPhc1 across all tissues, with the highest level of expression observed in the hepatopancreas. The expression pattern of PtPhc1 in response to Vibrio parahaemolyticus infection was clarified using RT-qPCR in swimming crabs. Notably, the expression peaked at 24 h, and increased 1435-fold compared to the control group in the hepatopancreas. While the expression level reached the maximum value at 72 h, which was 3.24 times higher than that of the control group in hemocytes. Remarkably, the reduction in PtPhc1 expression led to a noteworthy 30% increase in the mortality rate of P. trituberculatus when exposed to V. parahaemolyticus. In addition, in vitro bacterial inhibition assays exhibited a dose-dependent suppression of bacterial proliferation by recombinant PtPhc1 protein, with a notable inhibition rate of 48.33% against V. parahaemolyticus at a concentration of 0.03 mg/mL. To the best of our knowledge, the results establish the function of pseudohaemocyanin in immunity for the first time, contributing to a deeper comprehension of innate immune regulatory mechanisms in aquatic organisms and advancing strategies for disease-resistant breeding.

OmpU and OmpC are the key OMPs for Litopenaeus vannamei hemocyanin recognizes Vibrio parahaemolyticus

Hemocyanin is a multifunctional protein present in arthropods and mollusks, responsible for oxygen transport and participating in multiple roles of immune defense including antibacterial activity. However, the molecular basis of how hemocyanin recognizes pathogens and exerts antibacterial activity remains poorly understood. In the present study, the pull-down assay was used to isolate Vibrio parahaemolyticus outer membrane proteins (OMPs) that bind to Litopenaeus vannamei hemocyanin. Two interacting OMPs bands were determined as OmpC and OmpU, and the heterogeneous interaction between hemocyanin and the two OMPs was further confirmed by far-Western blot. After construction of ompC and ompU deletion mutants, we found that the agglutinating activity and antibacterial activity of hemocyanin significantly decreased compared to the wild-type strain. After hemocyanin treatment, we identified four intracellular proteins of V. parahaemolyticus, including fructose-bisphosphate aldolase and ribosomal proteins could interact with rOmpC and rOmpU, respectively. Furthermore, we found that the mRNA levels of ompC, ompU, fbaA, rpsB and rpsC significantly decreased after hemocyanin treatment. These findings indicated that OmpC and OmpU are the key targets for L. vannamei hemocyanin recognize pathogens and exert its antibacterial activity.

The evolutionary adaptation of shrimp hemocyanin subtypes and the consequences on their structure and functions

Hemocyanin is the main respiratory protein of arthropods and is formed by hexameric and/or oligomeric subunits. Due to changes in the living environment and gene rearrangement, various hemocyanin subtypes and subunits evolved in crustaceans. This paper reviews the various hemocyanin subtypes and isoforms in shrimp and analyses published genomic data of sixteen hemocyanin family genes from Litopenaeus vannamei to explore the evolution of hemocyanin genes, subunits, and protein structure. Analysis of hemocyanin subtypes distribution and structure in various tissues was also performed and related to multiple and tissue-specific functions, i.e., immunological activity, immune signaling, phenoloxidase activity, modulation of microbiota homeostasis, and energy metabolism. The functional diversity of shrimp hemocyanin due to molecular polymorphism, transcriptional regulation, alternative splicing, degradation into functional peptides, interaction with other proteins or genes, and structural differences will also be highlighted for future research. Inferences would be drawn from other crustaceans to explain how evolution has changed the structure-function of hemocyanin and its implication for evolutionary research into the multifunctionality of hemocyanin and other related proteins in shrimp.

Antibacterial Action of Protein Fraction Isolated from Rapana venosa Hemolymph against Escherichia coli NBIMCC 8785

Natural products and especially those from marine organisms are being intensively explored as an alternative to synthetic antibiotics. However, the exact mechanisms of their action are not yet well understood. The molecular masses of components in the hemolymph fraction with MW 50-100 kDa from Rapana venosa were determined using ImageQuant™ TL v8.2.0 software based on electrophoretic analysis. Mainly, three types of compounds with antibacterial potential were identified, namely proteins with MW at 50.230 kDa, 62.100 kDa and 93.088 kDa that were homologous to peroxidase-like protein, aplicyanin A and L-amino acid oxidase and functional units with MW 50 kDa from R. venous hemocyanin. Data for their antibacterial effect on Escherichia coli NBIMCC 8785 were obtained by CTC/DAPI-based fluorescent analysis (analysis based on the use of a functional fluorescence probe). The fluorescent analyses demonstrated that a 50% concentration of the fraction with MW 50-100 kDa was able to eliminate 99% of the live bacteria. The antimicrobial effect was detectable even at a 1% concentration of the active compounds. The bacteria in this case had reduced metabolic activity and a 24% decreased size. The fraction had superior action compared with another mollusc product-snail slime-which killed 60% of the E. coli NBIMCC 8785 cells at a 50% concentration and had no effect at a 1% concentration. The obtained results demonstrate the high potential of the fraction with MW 50-100 kDa from R. venosa to eliminate and suppress the development of Escherichia coli NBIMCC 8785 bacteria and could be applied as an appropriate component of therapeutics with the potential to replace antibiotics to avoid the development of antibiotic resistance.

Prediction and bioactivity of small-molecule antimicrobial peptides from Protaetia brevitarsis Lewis larvae

Antimicrobial peptides (AMPs) are widely recognized as promising natural antimicrobial agents. Insects, as the group of animals with the largest population, have great potential as a source of AMPs. Thus, it is worthwhile to investigate potential novel AMPs from Protaetia brevitarsis Lewis larvae, which is a saprophagous pest prevalent in China. In this study, comparing the whole-genome sequence of Protaetia brevitarsis Lewis larvae with the Antimicrobial Peptide Database (APD3) led to the identification of nine peptide templates that were potentially AMPs. Next, based on the peptide templates, 16 truncated sequences were predicted to the AMPs by bioinformatics software and then underwent structural and physicochemical property analysis. Thereafter, candidate small-molecule AMPs were artificially synthesized and their minimal inhibitory concentration (MIC) values were assessed. A candidate peptide, designated FD10, exhibited strong antimicrobial activity against both bacteria and fungi comprising Escherichia coli (MIC: 8 μg/mL), Pseudomonas aeruginosa (MIC: 8 μg/mL), Bacillus thuringiensis (MIC: 8 μg/mL), Staphylococcus aureus (MIC: 16 μg/mL), and Candida albicans (MIC: 16 μg/mL). Additionally, two other candidate peptides, designated FD12 and FD15, exhibited antimicrobial activity against both E. coli (MIC: both 32 μg/mL) and S. aureus (MIC: both 16 μg/mL). Moreover, FD10, FD12, and FD15 killed almost all E. coli and S. aureus cells within 1 h, and the hemolytic effect of FD10 (0.31%) and FD12 (0.40%) was lower than that of ampicillin (0.52%). These findings indicate that FD12, FD15, and especially FD10 are promising AMPs for therapeutic application. This study promoted the development of antibacterial drugs and provided a theoretical basis for promoting the practical application of antimicrobial peptides in the Protaetia brevitarsis Lewis larvae.

EAACI Molecular Allergology User's Guide 2.0

Since the discovery of immunoglobulin E (IgE) as a mediator of allergic diseases in 1967, our knowledge about the immunological mechanisms of IgE-mediated allergies has remarkably increased. In addition to understanding the immune response and clinical symptoms, allergy diagnosis and management depend strongly on the precise identification of the elicitors of the IgE-mediated allergic reaction. In the past four decades, innovations in bioscience and technology have facilitated the identification and production of well-defined, highly pure molecules for component-resolved diagnosis (CRD), allowing a personalized diagnosis and management of the allergic disease for individual patients. The first edition of the "EAACI Molecular Allergology User's Guide" (MAUG) in 2016 rapidly became a key reference for clinicians, scientists, and interested readers with a background in allergology, immunology, biology, and medicine. Nevertheless, the field of molecular allergology is moving fast, and after 6 years, a new EAACI Taskforce was established to provide an updated document. The Molecular Allergology User's Guide 2.0 summarizes state-of-the-art information on allergen molecules, their clinical relevance, and their application in diagnostic algorithms for clinical practice. It is designed for both, clinicians and scientists, guiding health care professionals through the overwhelming list of different allergen molecules available for testing. Further, it provides diagnostic algorithms on the clinical relevance of allergenic molecules and gives an overview of their biology, the basic mechanisms of test formats, and the application of tests to measure allergen exposure.

Health-Promoting Additives Supplemented in Inert Microdiets for Whiteleg Shrimp (Penaeus vannamei) Post-Larvae: Effects on Growth, Survival, and Health Status

Dietary additives have the potential to stimulate the whiteleg shrimp immune system, but information is scarce on their use in diets for larval/post-larval stages. The potential beneficial effects of vitamins C and E, β-glucans, taurine, and methionine were evaluated. Four experimental microdiets were tested: a positive control diet (PC); the PC with decreased levels of vitamin C and E as negative control (NC); the PC with increased taurine and methionine levels (T + M); and the PC supplemented with β-glucans (BG). No changes in growth performance and survival were observed. However, post-larvae shrimp fed the NC had lower relative expressions of pen-3 than those fed the PC, suggesting that lower levels of vitamins C and E may impact the shrimp immune status. Lipid peroxidation levels dropped significantly in the BG compared to the PC, indicating that β-glucans improved the post-larvae antioxidant mechanisms. Furthermore, when compared with the NC diet, PL fed with BG showed significant increases in tGSH levels and in the relative expression of crus and pen-3, suggesting a synergistic effect between vitamins C and E and β-glucans. Amongst the additives tested, β-glucans seems to be the most promising even when compared to a high-quality control diet.

Preparation, Purification and Characterization of Antibacterial and ACE Inhibitory Peptides from Head Protein Hydrolysate of Kuruma Shrimp, Marsupenaeus japonicus

Kuruma shrimp (Marsupenaeus japonicus) heads, as the main by-product of the seafood processing industry, are rich in underutilized high-quality protein. After papain hydrolysis at 50 °C for 4 h, the protein hydrolysate of shrimp heads was found to show notable antibacterial and angiotensin I-converting enzyme (ACE) inhibitory activities. After purification using two stages of revered-phase high-performance liquid chromatography (RP-HPLC), the antibacterial peptide VTVP and the ACE inhibitory peptide ARL/I were successfully identified from most active fractions by LC-MS/MS. Peptide VTVP was a desirable hydrophobic peptide, with a MIC value in the range from 1.62 to 8.03 mM against all tested pathogens. Peptide ARL/I exhibited potent ACE inhibitory activity, with an IC50 value of 125.58 µM, and was found to be a competitive inhibitor based on the Lineweaver-Burk plot. Moreover, the result of the molecular docking simulation indicated that the interaction binding between ARL/I and ACE was mainly stabilized by hydrogen bonds, as well as forming a coordinate bond with the Zn²⁺ site. The purified peptides did not show hemolytic activity toward rabbit erythrocytes. To sum up, the bioactive peptides isolated from shrimp heads could be applicable for food or pharmaceutical areas as promising ingredients.

Efficacy of natural antimicrobial peptides versus peptidomimetic analogues: a systematic review

Aims: This systematic review was carried out to determine whether synthetic peptidomimetics exhibit significant advantages over antimicrobial peptides in terms of in vitro potency. Structural features - molecular weight, charge and length - were examined for correlations with activity. Methods: Original research articles reporting minimum inhibitory concentration  values against Escherichia coli, indexed until 31 December 2020, were searched in PubMed/ScienceDirect/Google Scholar and evaluated using mixed-effects models. Results: In vitro antimicrobial activity of peptidomimetics resembled that of antimicrobial peptides. Net charge significantly affected minimum inhibitory concentration values (p < 0.001) with a trend of 4.6% decrease for increments in charge by +1. Conclusion: AMPs and antibacterial peptidomimetics exhibit similar potencies, providing an opportunity to exploit the advantageous stability and bioavailability typically associated with peptidomimetics.

CAMPR4: a database of natural and synthetic antimicrobial peptides

There has been an exponential increase in the design of synthetic antimicrobial peptides (AMPs) for its use as novel antibiotics. Synthetic AMPs are substantially enriched in residues with physicochemical properties known to be critical for antimicrobial activity; such as positive charge, hydrophobicity, and higher alpha helical propensity. The current prediction algorithms for AMPs have been developed using AMP sequences from natural sources and hence do not perform well for synthetic peptides. In this version of CAMP database, along with updating sequence information of AMPs, we have created separate prediction algorithms for natural and synthetic AMPs. CAMPR4 holds 24243 AMP sequences, 933 structures, 2143 patents and 263 AMP family signatures. In addition to the data on sequences, source organisms, target organisms, minimum inhibitory and hemolytic concentrations, CAMPR4 provides information on N and C terminal modifications and presence of unusual amino acids, as applicable. The database is integrated with tools for AMP prediction and rational design (natural and synthetic AMPs), sequence (BLAST and clustal omega), structure (VAST) and family analysis (PRATT, ScanProsite, CAMPSign). The data along with the algorithms of CAMPR4 will aid to enhance AMP research. CAMPR4 is accessible at http://camp.bicnirrh.res.in/.

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.

Functional Characterization, Antimicrobial Effects, and Potential Antibacterial Mechanisms of NpHM4, a Derived Peptide of Nautilus pompilius Hemocyanin

Hemocyanins present in the hemolymph of invertebrates are multifunctional proteins that are responsible for oxygen transport and play crucial roles in the immune system. They have also been identified as a source of antimicrobial peptides during infection in mollusks. Hemocyanin has also been identified in the cephalopod ancestor Nautilus, but antimicrobial peptides derived from the hemocyanin of Nautilus pompilius have not been reported. Here, the bactericidal activity of six predicted peptides from N. pompilius hemocyanin and seven mutant peptides was analyzed. Among those peptides, a mutant peptide with 15 amino acids (1RVFAGFLRHGIKRSR15), NpHM4, showed relatively high antibacterial activity. NpHM4 was determined to have typical antimicrobial peptide characteristics, including a positive charge (+5.25) and a high hydrophobic residue ratio (40%), and it was predicted to form an alpha-helical structure. In addition, NpHM4 exhibited significant antibacterial activity against Gram-negative bacteria (MBC = 30 μM for Vibrio alginolyticus), with no cytotoxicity to mammalian cells even at a high concentration of 180 µM. Upon contact with V. alginolyticus cells, we confirmed that the bactericidal activity of NpHM4 was coupled with membrane permeabilization, which was further confirmed via ultrastructural images using a scanning electron microscope. Therefore, our study provides a rationalization for the development and optimization of antimicrobial peptide from the cephalopod ancestor Nautilus, paving the way for future novel AMP development with broad applications.

Prediction and characterization of a novel hemoglobin-derived mutant peptide (mTgHbP7) from Tegillarca granosa

The hemoglobin (Hb) is identified in Tegillarca granosa and its derived peptides have been proved to possess antibacterial activity against gram-positive and gram-negative bacteria. In this study, we identified a series of novel antimicrobial peptides (AMPs) and artificially mutated AMPs derived from subunits of T. granosa Hbs, among which, a mutant T. granosa hemoglobin peptide (mTgHbP) mTgHbP7, was proved to possess predominant antibacterial activity against three bacteria strains (Vibrio alginolyticus, V. parahaemolyticus and Escherichia coli). Besides, mTgHbP7 was predicted to form α-helical structure, which was known to be an important feature of bactericidal AMPs. Furthermore, upon contact with HEK293 cell line, we confirmed that mTgHbP7 had no cytotoxicity to mammalian cell even at a high concentration of 160 μM. Therefore, the findings reported here provide a rationalization for antimicrobial peptide prediction and optimization from mollusk hemoglobin, which will be useful for future development of antimicrobial agents.

LvHemB1, a novel cationic antimicrobial peptide derived from the hemocyanin of Litopenaeus vannamei, induces cancer cell death by targeting mitochondrial voltage-dependent anion channel 1

Current cancer treatment regimens such as chemotherapy and traditional chemical drugs have adverse side effects including the appearance of drug-resistant tumor cells. For these reasons, it is imperative to find novel therapeutic agents that overcome these factors. To this end, we explored a cationic antimicrobial peptide derived from Litopenaeus vannamei hemocyanin (designated LvHemB1) that induces cancer cell death, but sparing normal cells. LvHemB1 inhibits the proliferation of human cervical (HeLa), esophageal (EC109), hepatocellular (HepG2), and bladder (EJ) cancer cell lines, but had no significant effect on normal liver cell lines (T-antigen-immortalized human liver epithelial (THLE-3) cells). In addition to its antiproliferative effects, LvHemB1 induced apoptosis, by permeating cells and targeting mitochondrial voltage-dependent anion channel 1 (VDAC1). Colocalization studies revealed the localization of LvHemB1 in mitochondria, while molecular docking and pull-down analyses confirmed LvHemB1-VDAC1 interaction. Moreover, LvHemB1 causes loss in mitochondrial membrane potential and increases levels of reactive oxygen species (ROS) and apoptotic proteins (caspase-9, caspase-3, and Bax (Bcl-2-associated X)), which results in mitochondrial-mediated apoptosis. Thus, peptide LvHemB1 has the potential of being used as an anticancer agent due to its antiproliferation effect and targeting to VDAC1 to cause mitochondrial dysfunction in cancer cells, as well as its ability to induce apoptosis by increasing ROS levels, and the expression of proapoptotic proteins.

Protein Diversity and Immune Specificity of Hemocyanin From Shrimp Litopenaeus vannamei

Hemocyanin is an important non-specific innate immune defense molecule with phenoloxidase, antiviral, antibacterial, hemolytic, and antitumor activities. To better understand the mechanism of functional diversity, proteomics approach was applied to characterize hemocyanin (HMC) expression profiles from Litopenaeus vannamei. At first, hemocyanin was purified by Sephadex G-100 and DEAE-cellulose (DE-52) columns from shrimp serum, and 34 protein spots were identified as HMC on the 2-DE gels. Furthermore, we found that 9 HMC spots about 75 or 77 kDa were regulated by Streptococcus agalactiae and Vibrio parahaemolyticus infection at 6, 12, and 24 h. In addition, 6 different pathogen-binding HMC fractions, viz., HMC-Mix, HMC-Vp, HMC-Va, HMC-Vf, HMC-Ec, and HMC-Sa, showed different agglutinative and antibacterial activities. Moreover, lectin-blotting analysis showed significant differences in glycosylation level among HMC isomers and bacteria-binding HMC fractions. Particularly, the agglutinative activities of the HMC fractions were almost completely abolished when HMC was deglycosylated by O-glycosidase, which suggest that O-linked sugar chains of HMC played important roles in the innate immune recognition. Our findings demonstrated for the first time that L. vannamei HMC had molecular diversity in protein level, which is closely associated with its ability to recognize diverse pathogens, whereas glycan modification probably contributed to HMC’s diversity and multiple immune activities.

Aeromonas hydrophila associated with red spot disease in Macrobrachium nipponense and host immune-related gene expression profiles

In September 2018, a serious disease causing high mortality with red spot syndrome occurred in a Macrobrachium nipponense aquaculture farm in Jintan County, Jiangsu Province, China. In this study, a pathogenic isolate 5-S3 was isolated from diseased M. nipponense and was identified as Aeromonas hydrophila by phenotypically and molecularly. The pathogenicity of the isolate 5-S3 to M. nipponense was determined by challenge experiments. Results of artificial challenge showed A. hydrophila was pathogenic to M. nipponense, the LD₅₀ was 9.58 × 10⁴ CFU/mL, and histopathological analysis revealed that the hepatopancreas of infected M. nipponense exhibited obvious inflammatory responses to A. hydrophila infection. The isolate showed significant phenotypical activities such as the lecithinase, esterase, caseinase and hemolysin which are indicative of their virulence potential. Besides, virulence genes such as aerA, act, fla, ahpβ, alt, lip, eprCAI, hlyA, acg and gcaT were detected in the isolate 5-S3. Subsequently, the immune-related genes expression in M. nipponense were evaluated by quantitative real-time PCR (qRT-PCR), and the results showed that the expression levels of dorsal, relish, crustin1, crustin2, anti-lipopolysaccharide factors 1 (ALF1), anti-lipopolysaccharide factors 2 (ALF2), hemocyanin, i-lysozyme and prophenoloxidase were significantly up-regulated in hepatopancreas of M. nipponense after A. hydrophila infection, the stat, p38, crustin3, anti-lipopolysaccharide factors 3 (ALF3) genes had no significant change during the infection. The present results reveal that A. hydrophila was an etiological agent causing red spot syndrome and mass mortality of M. nipponense and the influence of A. hydrophila infection on host immune genes.

Antichagasic effect of hemocyanin derived from antimicrobial peptides of penaeus monodon shrimp

Trypanosoma cruzi, the etiological agent of Chagas disease, is responsible for the infection of millions of people worldwide and it is a public health problem, without an effective cure. Four fragments with antimicrobial potential from the hemocyanin of Penaeus monodon shrimp were identified using a computer software AMPA. The present study aimed to evaluate the antichagasic effect of these four peptides (Hmc364-382, Hmc666-678, Hmc185-197 and Hmc476-498). The peptides were tested against the epimastigote, trypomastigote and amastigote forms of Trypanosoma cruzi Y strain (benznidazole-resistant strain) and cytotoxicity in mammalian cells was evaluated against LLC-MK2 lineage cells. Two fragments (Hmc364-382, Hmc666-678) showed activity against the epimastigote and trypomastigote forms and their selectivity index (SI) was calculated. The Hmc364-382 peptide was considered the most promising (SI > 50) one and it was used for further studies, using flow cytometry analyses with specific molecular probes and scanning electron microscopy (SEM). Hmc364-382 was able to induce cell death in T. cruzi through necrosis, observed by loss of membrane integrity in flow cytometry analyses and pore formation in SEM. Overall, Hmc364-382 open perspectives to the development of new antichagasic agents.

Maturation of an Antimicrobial Peptide Inhibits Aeromonas hydrophila Infection in Crayfish

Rapid synthesis and release of active antimicrobial peptides (AMPs) is an important strategy in innate immune. Processing of the precursor into the active form is a common posttranslational modification of AMPs in mammals. However, in invertebrates, the mechanism of AMP maturation is largely unknown. In the current study, to our knowledge, a novel potential AMP, designated as PcnAMP, was identified because of its significant induction by bacterial infection in the red swamp crayfish (Procambarus clarkii). PcnAMP was cleaved into a short fragment postinfection. Using the purified native peptide, this cleavage was found to be mediated by trypsin after synthesis. Proteolysis produced an N-terminal peptide that exerted the antibacterial function. Although the N-terminal peptide did not show significant similarity to any other sequences, it was predicted to have an overall helical structure and high amphipathicity, both of which are typical features of many AMPs. The N-terminal active peptide exhibited a wide spectrum of antimicrobial activity. Atomic force microscope imaging and flow cytometry analysis showed that treatment with the active form of PcnAMP led to the collapse of the bacterial cell wall and permeabilization of the bacterial cell membrane. Thus, this study provided a new candidate for therapeutic agent development, and revealed new insights into the maturation of AMPs in invertebrates.

Effects of Vibro harveyi and Staphyloccocus aureus infection on hemocyanin synthesis and innate immune responses in white shrimp Litopenaeus vannamei

Hemocyanin, a multifunctional oxygen-carrying protein, has critical effects on immune defense in crustaceans. To explore the role of hemocyanin in anti-pathogen mechanism, effects of Vibrio harveyi (V. harvey) and Staphyloccocus aureus (S. aureus) on hemocyanin synthesis and innate immune responses were investigated in Litopenaeus vannamei (L. vannamei) during infection in vivo. Results showed that 10⁵ and 10⁶ cells mL^-1V. harveyi and 10⁶ cells mL^-1S. aureus significantly affected plasma hemocyanin concentration, hepatopancreas hemocyanin mRNA and subunits expressions, plasma phenol oxidase (PO), hemocyanin-derived PO (Hd-PO), antibacterial, and bacteriolytic activities during the experiment under bacterial stress, while these parameters did not change remarkably in control group. The concentration of hemocyanin in plasma fluctuated, with a minimum at 12 h and a maximum at 24 h. Moreover, the expression of hemocyanin mRNA peaked at 12 h, while the level of hemocyanin p75 and p77 subunits reached maximum at 24 h. Besides, plasma PO and Hd-PO activities peaked at 24 h, and antimicrobial and bacteriolytic activities peaked at 12 h and 24 h, respectively. In addition, 10⁵ cells mL^-1S. aureus had no significant effect on the synthesis of hemocyanin and prophenoloxidase activating (pro-PO) system, but significantly increased antimicrobial activity at 12 h and bacteriolytic activity at 24 h. Therefore, these results suggest that the hemocyanin synthesis was initiated after invasion of pathogen, and the newly synthesized hemocyanin, acted as an immune molecule, can exerts PO activity to regulate the immune defense in L. vannamei in vivo.

Collection of antimicrobial peptides database and its derivatives: Applications and beyond

Collection of antimicrobial peptides (CAMP), CAMPSign, and ClassAMP are open-access resources that have been developed to enhance research on antimicrobial peptides (AMPs). Comprehensive information on AMPs and machine learning-based predictive models are made available for users through these resources. As of date, CAMP_R3 has 10,247 sequences, 757 structures, and 114 family-specific signatures of AMPs along with associated tools for AMP sequence and structure analysis. CAMPSign uses family-specific sequence conservation, in the form of patterns and hidden Markov models for identification of AMPs. ClassAMP can be used to classify AMPs as antibacterial, antifungal, or antiviral based on sequence information. Here we describe CAMP and its derivatives and illustrate, with a few examples, the contribution of these online resources to the advancement of our current understanding of AMPs.

Litopenaeus vannamei attenuates white spot syndrome virus replication by specific antiviral peptides generated from hemocyanin

Recent studies have shown that hemocyanin plays immune-related functions apart from its canonical respiratory function. While shrimp hemocyanin is found to generate antimicrobial peptides, antiviral related peptides have not been reported. In the present study, the serum of white spot syndrome virus (WSSV) infected Litopenaeus vannamei analyzed by two-dimensional gel electrophoresis, revealed 45 consistently down-regulated protein spots and 10 up-regulated protein spots. Five of the significantly up-regulated spots were identified as hemocyanin derived peptides. One of the five peptides, designated LvHcL48, was further characterized by analyzing its primary sequence via Edman N-terminal sequencing, C-terminal sequencing and amino acid sequence alignment. LvHcL48 was found to be a 79 amino acid fragment (aa584-662) from the C-terminal domain of L. vannamei hemocyanin protein (ADZ15149). Both in vivo and in vitro functional studies revealed that LvHcL48 has immunological activities, as recombinant LvHcL48 protein (rLvHcL48) significantly inhibited the transcription of the WSSV genes wsv069 and wsv421 coupled with a significant reduction in WSSV copy numbers. Further analysis showed that LvHcL48 could interact with the WSSV envelope protein 28 (VP28). Our present data therefore reveals the generation of an antiviral hemocyanin derived peptide LvHcL48 from WSSV infected shrimp, which binds to the envelope protein VP28 of WSSV.

Discovery and identification of antimicrobial peptides in Sichuan pepper (Zanthoxylum bungeanum Maxim) seeds by peptidomics and bioinformatics

Antimicrobial peptides (AMPs) have generated growing attention because of the increasing bacterial resistance. However, the discovery and identification of AMPs have proven to be challenging due to the complex purification procedure associated with conventional methods. For the reasons given above, it is necessary to explore more efficient ways to obtain AMPs. We established a new method for discovery and identification of novel AMPs by proteomics and bioinformatics from Zanthoxylum bungeanum Maxim seeds protein hydrolysate directly. This process was initially achieved by employing ultra-performance liquid chromatography-electrospray ionization-mass spectrometry/mass (UPLC-ESI-MS/MS) spectrometry to identify peptides derived from Z. bungeanum Maxim seed protein hydrolysates. Three online servers were introduced to predict potential AMPs. Sixteen potential AMPs ranging from 1.5 to 2.7 kDa were predicted and chemically synthesized, one of which, designated NP-6, inhibited activity against all the tested strains according to antimicrobial assay. Time-killing assay indicated that NP-6 could quickly kill almost all the Escherichia coli within 180 min and Staphylococcus aureus at 360 min. Moreover, the simulation 3D structure of NP-6 was consisted of α-helix and random coil, and this was verified by circular dichroism (CD) spectra. At last, the scanning electron microscope (SEM) images of E. coli and S. aureus treated by NP-6 demonstrated that NP-6 had a significant effect on bacteria cell morphology. Our findings provide an efficient approach for discovery of AMPs, and Z. bungeanum Maxim seeds may be a nature resource to extract antimicrobial agents.

A Litopenaeus vannamei Hemocyanin-Derived Antimicrobial Peptide (Peptide B11) Attenuates Cancer Cells' Proliferation

Antimicrobial peptides play important roles in the immune response to pathogens and tumor cells; for this reason, they are being exploited for therapeutic use. In this study, we describe a Litopenaeus vannamei hemocyanin-derived peptide, denoted B11, which shares similar features with other anticancer peptides and attenuates the proliferation of cancer cells. Cell viability assay revealed that B11 significantly inhibited the proliferation of human cervical (HeLa), human hepatocellular carcinoma (HepG2), and human esophageal cancer (EC109) cancer cell lines, but not normal liver cell lines (T-antigen-immortalized human liver epithelial (THLE) cells or THLE-3), by inducing morphological changes, nuclear condensation, and margination, features which are indicative of apoptosis. Besides, peptide B11-induced apoptosis was confirmed by isothiocyanate-labeled Annexin V/propidium iodide (Annexin V-FITC/PI) double staining of HeLa cells. Moreover, cell uptake studies, confocal microscopy, and Western blot analysis revealed that rhodamine-labeled B11 permeated HeLa cells and localized to the mitochondria, causing mitochondria dysfunction through lost mitochondrial membrane potential, which consequently triggered the induction of apoptosis. Increased expression levels of caspase-9, caspase-3, and Bax (Bcl-2-associated X) proteins, coupled with a decrease in Bcl-2 (B-cell lymphoma 2) protein, confirmed that peptide B11 induced apoptosis via the mitochondrial pathway. Thus, the hemocyanin-derived peptide, B11, inhibits the proliferation of cancer cells by causing mitochondrial dysfunction and inducing apoptotic cell death, for which reason it could be explored as an anticancer peptide.