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

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.

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.

Penaeid shrimp counteract high ammonia stress by generating and using functional peptides from hemocyanin, such as HMCs27

Agricultural and anthropogenic activities release high ammonia levels into aquatic ecosystems, severely affecting aquatic organisms. Penaeid shrimp can survive high ammonia stress conditions, but the underlying molecular mechanisms are unknown. Here, total hemocyanin and oxyhemocyanin levels decreased in Penaeus vannamei plasma under high ammonia stress. When shrimp were subjected to high ammonia stress for 12 h, 24 hemocyanin (HMC) derived peptides were identified in shrimp plasma, among which one peptide, designated as HMCs27, was chosen for further analysis. Shrimp survival was significantly enhanced after treatment with the recombinant protein of HMCs27 (rHMCs27), followed by high ammonia stress. Transcriptome analysis of shrimp hepatopancreas after treatment with or without rHMCs27 followed by high ammonia stress revealed 973 significantly dysregulated genes, notable among which were genes involved in oxidation and metabolism, such as cytochrome C, catalase (CAT), isocitrate dehydrogenase, superoxide dismutase (SOD), trypsin, chymotrypsin, glutathione peroxidase, glutathione s-transferase (GST), and alanine aminotransferase (ALT). In addition, levels of key biochemical indicators, such as SOD, CAT, and total antioxidant capacity (T-AOC), were significantly enhanced, whereas hepatopancreas malondialdehyde levels and plasma pH, NH3, GST, and ALT levels were significantly decreased after rHMCs27 treatment followed by high ammonia stress. Moreover, high ammonia stress induced hepatopancreas tissue injury and apoptosis, but rHMCs27 treatment ameliorated these effects. Collectively, the current study revealed that in response to high ammonia stress, shrimp generate functional peptides, such as peptide HMCs27 from hemocyanin, which helps to attenuate the ammonia toxicity by enhancing the antioxidant system and the tricarboxylic acid cycle to decrease plasma NH3 levels and pH.

Marine Invertebrate Antimicrobial Peptides and Their Potential as Novel Peptide Antibiotics

Marine invertebrates constantly interact with a wide range of microorganisms in their aquatic environment and possess an effective defense system that has enabled their existence for millions of years. Their lack of acquired immunity sets marine invertebrates apart from other marine animals. Invertebrates could rely on their innate immunity, providing the first line of defense, survival, and thriving. The innate immune system of marine invertebrates includes various biologically active compounds, and specifically, antimicrobial peptides. Nowadays, there is a revive of interest in these peptides due to the urgent need to discover novel drugs against antibiotic-resistant bacterial strains, a pressing global concern in modern healthcare. Modern technologies offer extensive possibilities for the development of innovative drugs based on these compounds, which can act against bacteria, fungi, protozoa, and viruses. This review focuses on structural peculiarities, biological functions, gene expression, biosynthesis, mechanisms of antimicrobial action, regulatory activities, and prospects for the therapeutic use of antimicrobial peptides derived from marine invertebrates.

The mechanisms and factors that induce trained immunity in arthropods and mollusks

Besides dividing the organism's immune system into adaptive and innate immunity, it has long been thought that only adaptive immunity can establish immune memory. However, many studies have shown that innate immunity can also build immunological memory through epigenetic reprogramming and modifications to resist pathogens' reinfection, known as trained immunity. This paper reviews the role of mitochondrial metabolism and epigenetic modifications and describes the molecular foundation in the trained immunity of arthropods and mollusks. Mitochondrial metabolism and epigenetic modifications complement each other and play a key role in trained immunity.

A Novel Hemocyte-Specific Small Protein Participates in White Spot Syndrome Virus Infection via Binding to Viral Envelope Protein

Hemocytes are essential components of the immune system against invading pathogens in shrimp. Many uncharacterized transcripts exist in hemocytes but the knowledge of them is very limited. In the present study, we identified a novel small protein from the uncharacterized transcripts in hemocytes of Litopenaeus vannamei. This transcript was specifically expressed in hemocytes and encoded a novel secretory protein, which was designated as hemocyte-specific small protein (LvHSSP). The expression level of LvHSSP was significantly up-regulated in the hemocytes of shrimp infected with white spot syndrome virus (WSSV). After knockdown of LvHSSP by RNA interference, the WSSV copy number in shrimp decreased significantly. Conversely, WSSV copy number increased in shrimp when they were infected by WSSV after incubation with recombinant LvHSSP protein. These results suggested that LvHSSP might promote viral infection in shrimp. Immunocytochemical assay showed that the recombinant LvHSSP protein was located on the membrane of hemocytes. Co-IP results showed that LvHSSP could interact with VP26, the main envelope protein of WSSV, suggesting that LvHSSP might mediate WSSV adhesion and entry into host cells by binding to viral envelope protein. Meanwhile, the total hemocyte counts were significantly decreased after LvHSSP knockdown while increased after supplementing with recombinant LvHSSP protein, supporting the idea of hemocytes as the carrier for systemic dissemination of WSSV. This study reported a novel small protein in hemocytes, which modulated the viral infection in shrimp. Our results will enrich the knowledge of invertebrate innate immunity and provide a new field in the study of hemocyte function.

Resistance to white spot syndrome virus in the European shore crab is associated with suppressed virion trafficking and heightened immune responses

Introduction

All decapod crustaceans are considered potentially susceptible to White Spot Syndrome Virus (WSSV) infection, but the degree of White Spot Disease (WSD) susceptibility varies widely between species. The European shore crab Carcinus maenas can be infected with the virus for long periods of time without signs of disease. Given the high mortality rate of susceptible species, the differential susceptibility of these resistant hosts offers an opportunity to investigate mechanisms of disease resistance.

Methods

Here, the temporal transcriptional responses (mRNA and miRNA) of C. maenas following WSSV injection were analysed and compared to a previously published dataset for the highly WSSV susceptible Penaeus vannamei to identify key genes, processes and pathways contributing to increased WSD resistance.

Results

We show that, in contrast to P. vannamei, the transcriptional response during the first 2 days following WSSV injection in C. maenas is limited. During the later time points (7 days onwards), two groups of crabs were identified, a recalcitrant group where no replication of the virus occurred, and a group where significant viral replication occurred, with the transcriptional profiles of the latter group resembling those of WSSV-susceptible species. We identify key differences in the molecular responses of these groups to WSSV injection.

Discussion

We propose that increased WSD resistance in C. maenas may result from impaired WSSV endocytosis due to the inhibition of internal vesicle budding by dynamin-1, and a delay in movement to the nucleus caused by the downregulation of cytoskeletal transcripts required for WSSV cytoskeleton docking, during early stages of the infection. This response allows resistant hosts greater time to fine-tune immune responses associated with miRNA expression, apoptosis and the melanisation cascade to defend against, and clear, invading WSSV. These findings suggest that the initial stages of infection are key to resistance to WSSV in the crab and highlight possible pathways that could be targeted in farmed crustacean to enhance resistance to WSD.

Comprehensive analysis of lysine lactylation in Frankliniella occidentalis

Western flower thrips (Frankliniella occidentalis) are among the most important pests globally that transmit destructive plant viruses and infest multiple commercial crops. Lysine lactylation (Klac) is a recently discovered novel post-translational modification (PTM). We used liquid chromatography-mass spectrometry to identify the global lactylated proteome of F. occidentalis, and further enriched the identified lactylated proteins using Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO). In the present study, we identified 1,458 Klac sites in 469 proteins from F. occidentalis. Bioinformatics analysis showed that Klac was widely distributed in F. occidentalis proteins, and these Klac modified proteins participated in multiple biological processes. GO and KEGG enrichment analysis revealed that Klac proteins were significantly enriched in multiple cellular compartments and metabolic pathways, such as the ribosome and carbon metabolism pathways. Two Klac proteins were found to be involved in the regulation of the TSWV (Tomato spotted wilt virus) transmission in F. occidentalis. This study provides a systematic report and a rich dataset of lactylation in F. occidentalis proteome for potential studies on the Klac protein of this notorious pest.

Structure-Function Relationships of Oxygen Transport Proteins in Marine Invertebrates Enduring Higher Temperatures and Deoxygenation

AbstractPredictions for climate change-to lesser and greater extents-reveal a common scenario in which marine waters are characterized by a deadly trio of stressors: higher temperatures, lower oxygen levels, and acidification. Ectothermic taxa that inhabit coastal waters, such as shellfish, are vulnerable to rapid and prolonged environmental disturbances, such as heatwaves, pollution-induced eutrophication, and dysoxia. Oxygen transport capacity of the hemolymph (blood equivalent) is considered the proximal driver of thermotolerance and respiration in many invertebrates. Moreover, maintaining homeostasis under environmental duress is inextricably linked to the activities of the hemolymph-based oxygen transport or binding proteins. Several protein groups fulfill this role in marine invertebrates: copper-based extracellular hemocyanins, iron-based intracellular hemoglobins and hemerythrins, and giant extracellular hemoglobins. In this brief text, we revisit the distribution and multifunctional properties of oxygen transport proteins, notably hemocyanins, in the context of climate change, and the consequent physiological reprogramming of marine invertebrates.

Comparative Transcriptome Analysis Reveals That WSSV IE1 Protein Plays a Crucial Role in DNA Replication Control

For DNA viruses, the immediate-early (IE) proteins are generally essential regulators that manipulate the host machinery to support viral replication. Recently, IE1, an IE protein encoded by white spot syndrome virus (WSSV), has been demonstrated to function as a transcription factor. However, the target genes of IE1 during viral infection remain poorly understood. Here, we explored the host target genes of IE1 using RNAi coupled with transcriptome sequencing analysis. A total of 429 differentially expressed genes (DEGs) were identified from penaeid shrimp, of which 284 genes were upregulated and 145 genes were downregulated after IE1 knockdown. GO and KEGG pathway enrichment analysis revealed the identified DEGs are significantly enriched in the minichromosome maintenance (MCM) complex and DNA replication, indicating that IE1 plays a critical role in DNA replication control. In addition, it was found that Penaeus vannamei MCM complex genes were remarkably upregulated after WSSV infection, while RNAi-mediated knockdown of PvMCM2 reduced the expression of viral genes and viral loads at the early infection stage. Finally, we demonstrated that overexpression of IE1 promoted the expression of MCM complex genes as well as cellular DNA synthesis in insect High-Five cells. Collectively, our current data suggest that the WSSV IE1 protein is a viral effector that modulates the host DNA replication machinery for viral replication.

Antimicrobial peptides and their potential application in antiviral coating agents

Coronavirus pandemic has evidenced the importance of creating bioactive materials to mitigate viral infections, especially in healthcare settings and public places. Advances in antiviral coatings have led to materials with impressive antiviral performance; however, their application may face health and environmental challenges. Bio-inspired antimicrobial peptides (AMPs) are suitable building blocks for antimicrobial coatings due to their versatile design, scalability, and environmentally friendly features. This review presents the advances and opportunities on the AMPs to create virucidal coatings. The review first describes the fundamental characteristics of peptide structure and synthesis, highlighting the recent findings on AMPs and the role of peptide structure (α-helix, β-sheet, random, and cyclic peptides) on the virucidal mechanism. The following section presents the advances in AMPs coating on medical devices with a detailed description of the materials coated and the targeted pathogens. The use of peptides in vaccine formulations is also reported, emphasizing the molecular interaction of peptides with different viruses and the current clinical stage of each formulation. The role of several materials (metallic particles, inorganic materials, and synthetic polymers) in the design of antiviral coatings is also presented, discussing the advantages and the drawbacks of each material. The final section offers future directions and opportunities for using AMPs on antiviral coatings to prevent viral outbreaks.

Proteomics analysis reveals a critical role for the WSSV immediate-early protein IE1 in modulating the host prophenoloxidase system

White spot syndrome virus (WSSV) is a large enveloped double-stranded DNA virus that is a major impediment for shrimp aquaculture worldwide. So far, the mechanisms of WSSV-host interactions are ill-defined. Recent studies have revealed that IE1, an immediate-early protein encoded by WSSV, is a multifunctional modulator implicated in virus-host interactions. In this study, the biological functions of IE1 were further explored by identifying its interacting proteins using GST-pull down and mass spectrometry analysis. A total of 361 host proteins that potentially bind to IE1 were identified. Bioinformatics analysis revealed that the identified IE1-interacting proteins were key molecules involved in various signaling pathways such as prophenoloxidase (proPO) system, PI3K-AKT, MAPK, Focal adhesion, and cell cycle. Among these, the regulatory role of IE1 in the shrimp proPO system was further studied. The Co-immunoprecipitation (Co-IP) results confirmed that IE1 interacted with the Ig-like domain of Penaeus vannamei proPO or proPO-like proteins (proPO1/2 and hemocyanin). In addition, we found that in vivo RNAi mediated knockdown of IE1 reduced the viral genes expression and viral loads, as well as caused an increase in the PO activity of hemocytes during infection, whereas recombinant IE1 protein could inhibit the PO activity in a dose-dependent manner. Finally, our result demonstrated that WSSV could suppress the PO activity of hemocytes at the early infection stage. Collectively, our current data indicate that IE1 is a novel viral regulator that negatively modulates the shrimp proPO system, which provide additional insights into the biological functions of IE1 during WSSV infection.

Double‐edged sword role of shrimp miRNA explains an evolutionary language between shrimp‐pathogen interactions that unties the knot of shrimp infection

Shrimp production, using a small‐scale enclosed pond system, is a rapidly growing aquaculture sector, which is valued around USD 18.30 billion in 2020. Intensified shrimp culture leads to the outbreak of transmissible diseases to eventually cause a huge loss in the production process and thus the economy. Studies on microRNA (miRNA) reveal that miRNA has an influential role in the host‐pathogen interaction during an infection. Recently, shrimp miRNA has been shown to help pathogen‐like viruses for their replication and infection. Several shrimp miRNAs were reported to be involved in enhancing host immunity against viral infection, especially white spot syndrome virus (WSSV) infection and Vibrio infection caused by bacterial species, whereas some shrimp miRNAs were reported to be hijacked by WSSV and to enhance the viral replication and establish the infection in shrimp. This gives an insight into the double‐edged sword role played by shrimp miRNA during host‐pathogen interaction. In future, this role could be employed against the virus to strengthen the shrimp culture. In this review, we discuss the role of shrimp miRNA and their mechanism(s) associated with the establishment of host‐pathogen interaction during infection, which will reveal the complexity associated with shrimp infection.

The ARM repeat domain of hemocyanin interacts with MKK4 to modulate antimicrobial peptides expression

The mitogen-activated protein kinase (MAPK) intracellular signaling pathway mediates numerous biological processes, including antimicrobial immune response by inducing antimicrobial peptides (AMPs) production. Although MAPK signaling cascade proteins have been identified in penaeid shrimp, their modulation via the MKK4-p38-c-Jun cascade and effect on AMPs production is unknown. Here, we show that hemocyanin (PvHMC), antimicrobial peptides (anti-lipopolysaccharide factor, crustin, and penaeidins), and MKK4-p38-c-Jun cascade proteins are simultaneously induced by pathogens (Vibrio parahaemolyticus, Staphylococcus aureus, and white spot syndrome virus) in Penaeus vannamei. Intriguingly, knockdown of PvHMC with or without pathogen challenge attenuated the expression of MKK4-p38-c-Jun cascade proteins and their phosphorylation level, which consequently decreased AMPs expression. Further analysis revealed that PvHMC interacts via its armadillo (ARM) repeat domain with PvMKK4 to modulate the p38 MAPK signaling pathway. Thus, the ARM repeat domain enables penaeid shrimp hemocyanin to modulate AMPs expression during antimicrobial response by activating the p38 MAPK signaling pathway.

•

Pathogens induce hemocyanin, MKK4-p38-c-Jun proteins, and antimicrobial peptide genes

•

Hemocyanin modulates MKK4-p38-c-Jun cascade proteins to regulate AMPs gene expression

•

Hemocyanin interacts with MKK4 to modulate p38 MAPK signaling in penaeid shrimp

•

Deletion of the ARM repeat domain attenuates the interaction of hemocyanin with MKK4

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.

Antibacterial, Antibiofilm and Anti-Virulence Activity of Biactive Fractions from Mucus Secretion of Giant African Snail Achatina fulica against Staphylococcus aureus Strains

Staphylococcus aureus is an important etiological agent that causes skin infections, and has the propensity to form biofilms, leading to significant mortality and morbidity in patients with wounds. Mucus secretion from the Giant African snail Achatina fulica is a potential source of biologically active substances that might be an important source for new drugs to treat resistant and biofilm-forming bacteria such as S. aureus. This study evaluated the effect of semi-purified fractions from the mucus secretion of A. fulica on the growth, biofilm formation and virulence factors of S. aureus. Two fractions: FMA30 (Mw >30 kDa) and FME30 (Mw 30−10 kDa) exhibited antimicrobial activity against S. aureus with a MIC₅₀ of 25 and 125 µg/mL, respectively. An inhibition of biofilm formation higher than 80% was observed at 9 µg/mL with FMA30 and 120 µg/mL with FME30. Furthermore, inhibition of hemolytic and protease activity was determined using a concentration of MIC₂₀, and FME30 showed a strong inhibitory effect in the formation of clots. We report for the first time the effect of semi-purified fractions of mucus secretion of A. fulica on biofilm formation and activity of virulence factors such as α-hemolysin, coagulase and proteases produced by S. aureus strains.

Low-intensity ultrasound enhances the antimicrobial activity of neutral peptide TGH2 against Escherichia coli

In recent years, foodborne diseases caused by Escherichia coli are a major threat to the food industry and consumers. Antimicrobial peptides (AMPs) and ultrasound both have good inhibitory effects on E. coli. In this work, the mechanism of action and synergistic effect of an in silico predicted AMP, designated as TGH2 (AEFLREKLGDKCTDRHV), from the C-terminal sequence of Tegillarca granosa hemoglobin, combined with low-intensity ultrasound was explored. The minimal inhibitory concentration (MIC) of TGH2 on E. coli decreased by 4-fold to 31.25 μg/mL under 0.3 W/cm2 ultrasound treatment, while the time kill curve analysis showed that low-intensity ultrasound combined with peptide TGH2 had an enhanced synergistic bactericidal effect after 0.5 h. The permeability on E. coli cell membrane increased progressively during combined treatment with peptide TGH2 and low-intensity ultrasound, resulting in the leakage of intracellular solutes, as shown by transmission electron microscopy (TEM). Structural analysis using circular dichroism (CD) revealed that peptide TGH2 has an α-helical structure, showing a slight untwisting effect under 0.3 W/cm2 ultrasound treatment for 0.5 h. The findings here provide new insight into the potential application of ultrasound and AMPs combination in food preservation.

Antiviral peptides from aquatic organisms: Functionality and potential inhibitory effect on SARS-CoV-2

Several antiviral peptides (AVPs) from aquatic organisms have been effective in interfering with the actions of infectious viruses, such as Human Immunodeficiency Virus-1 and Herpes Simplex Virus-1 and 2. AVPs are able to block viral attachment or entry into host cells, inhibit internal fusion or replication events by suppressing viral gene transcription, and prevent viral infections by modulating host immunity. Therefore, as promising therapeutics, the potential of aquatic AVPs for use against the COVID-19 pandemic caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) is considered. At present no therapeutic drugs are yet available. A total of 32 AVPs derived from fish and shellfish species are discussed in this review paper with notes on their properties and mechanisms of action in the inhibition of viral diseases both in humans and animals, emphasizing on SARS-CoV-2. The molecular structure of novel SARS-CoV-2 with its entry mechanisms, clinical signs and symptoms are also discussed. In spite of only a few study of these AVPs against SARS-CoV-2, aquatic AVPs properties and infection pathways (entry, replication and particle release) into coronaviruses are linked in this paper to postulate an analysis of their potential but unconfirmed actions to impair SARS-CoV-2 infection in humans.

Litopenaeus vannamei Notch interacts with COP9 signalosome complex subunit 1 (CNS1) to negatively regulate the NF-κB pathway

Notch signaling pathway is a highly evolutionary conserved signaling pathway, which modulates many biological processes such as cell differentiation, tissue development and immune response. Our previous study revealed that Litopenaeus vannamei Notch (LvNotch) was involved in immune response by regulating reactive oxygen species (ROS) production in hemocytes. However, the immune regulatory networks mediated by LvNotch remain unclear in shrimp. In this study, 21 proteins that potentially interact with LvNotch were identified by GST pull-down and liquid chromatography tandem mass spectrometry (LC-MS/MS) analyses. Among these proteins, COP9 signalosome complex subunit 1 (CSN1) was chosen for further studies due to its putative role in immune response. The interaction between LvNotch and LvCSN1 was confirmed by Far-Western blot and GST pull-down analyses. In vivo knockdown of LvNotch resulted in an increase in LvCSN1 expression in hemocytes, which suggest that the COP9 signalosome complex might be negatively regulated by LvNotch. In addition, in vivo silencing of LvNotch upregulated the expression of LvDorsal, LvTNFSF and LvCrustin2 (NF-κB pathway related-genes), while their expression decreased after LvCSN1 depletion. Collectively, the current results indicate that LvNotch negatively regulates the NF-κB pathway by modulating LvCSN1 in shrimp. SIGNIFICANCE: Although the Notch signaling pathway has been implicated in the regulation of immune response in vertebrates and invertebrates, the functions and immune-related interacting networks of Notch in shrimp immune response remain unknown. In this study, twenty-one proteins including COP9 signalosome complex subunit 1 (CSN1) were identified as potential interacting partners of LvNotch. Further analysis revealed that LvNotch negatively regulates the NF-κB pathway by binding to CSN1 and modulating its expression. These findings for the first time suggest that the Notch signaling pathway has cross-talk with the NF-κB pathway in shrimp as part of the immune response.

A SNP of the hemocyanin gene (LvHc) is a marker for high growth and ammonia-tolerance in Pacific white shrimp Litopenaeus vannamei

Expression levels of hemocyanin (LvHc), activating transcription factor 4 (LvAtf4), glutathione S-transferase (LvGst), caspase 2 (LvCasp2) and anti-lipopolysaccharide factor (LvAlf) were examined in the hepatopancreas of Pacific white shrimp Litopenaeus vannamei juveniles exposed to a lethal concentration of ammonia-N (32.15 mg/l). The expression levels of all transcripts except LvAlf were significantly greater (P < 0.05) in tolerant shrimp (Lv-AT; N = 30) that survived up to 72 h post treatment (hpt) than in susceptible shrimp (Lv-AS24 and Lv-AS72; N = 45 and 15), that died within 24 h or between 24 and 72 hpt, respectively. Subsequently, effects of non-lethal concentrations of ammonia-N (control, 10 and 20 mg/l) on the expression of LvHc in juvenile shrimp were examined. Compared to the control, expression levels of LvHc transcripts in hemocytes and the hepatopancreas of tested shrimp changed after exposure to ammonia-N. One SNP (C > T₅₄₅) was found in the LvHc₃₂₂ gene segment. Real-time PCR amplification of specific alleles (real-time PASA) was developed for detection of C > T₅₄₅ genotypes. Juveniles in the lethal exposure test that carried a C/T₅₄₅ genotype showed a greater average body weight and total length (8.46 ± 0.36 g and 10.05 ± 0.16 cm) than those with a C/C₅₄₅ genotype (7.48 ± 0.31 g and 9.60 ± 0.13 cm) (P < 0.05). Similar results were found in the second generation (G2) of a growth-improved stock (3 and 4 families of BIOTEC-G2-L1 and BIOTEC-G2-L2) and in commercially farmed shrimp (2 groups). Accordingly, expression levels and SNP of LvHc can serve as markers for selection high growth performance in ammonia-tolerant L. vannamei.

In silico studies on the interaction of phage displayed biorecognition element (TFQAFDLSPFPS) with the structural protein VP28 of white spot syndrome virus

White spot disease caused by the white spot syndrome virus (WSSV) incurs a huge loss to the shrimp farming industry. Since no effective therapeutic measures are available, early detection and prevention of the disease are indispensable. Towards this goal, we previously identified a 12-mer phage displayed peptide (designated as pep28) with high affinity for VP28, the structural protein of the white spot syndrome virus (WSSV). The peptide pep28 was successfully used as a biorecognition probe in the lateral flow assay developed for rapid, on-site detection of WSSV. To unravel the structural determinants for the selective binding between VP28 and pep28, we used bioinformatics, structural modeling, protein-protein docking, and binding-free energy studies. We performed atomistic molecular dynamics simulations of pep28-pIII model totaling 300 ns timescale. The most representative pep28-pIII structure from the simulation was used for docking with the crystal structure of VP28. Our results reveal that pep28 binds in a surface groove of the monomeric VP28 β-barrel and makes several hydrogen bonds and non-polar interactions. Ensemble-based binding-free energy studies reveal that the binding is dominated by non-polar interactions. Our studies provide molecular level insights into the binding mechanism of pep28 with VP28, which explain why the peptide is selective and can assist in modifying pep28 for its practical use, both as a biorecognition probe and a therapeutic.

Ten-Year Research Update Review: Antiviral Activities from Marine Organisms

Oceans cover more than 70 percent of the surface of our planet and are characterized by huge taxonomic and chemical diversity of marine organisms. Several studies have shown that marine organisms produce a variety of compounds, derived from primary or secondary metabolism, which may have antiviral activities. In particular, certain marine metabolites are active towards a plethora of viruses. Multiple mechanisms of action have been found, as well as different targets. This review gives an overview of the marine-derived compounds discovered in the last 10 years. Even if marine organisms produce a wide variety of different compounds, there is only one compound available on the market, Ara-A, and only another one is in phase I clinical trials, named Griffithsin. The recent pandemic emergency caused by SARS-CoV-2, also known as COVID-19, highlights the need to further invest in this field, in order to shed light on marine compound potentiality and discover new drugs from the sea.

The sterol regulatory element binding protein homolog of Penaeus vannamei modulates fatty acid metabolism and immune response

The sterol regulatory element binding proteins (SREBPs) transcription factors family, which regulate the expression of genes involved in cellular lipid metabolism and homeostasis, have recently been implicated in various physiological and pathophysiological processes such as immune regulation and inflammation in vertebrates. Consistent with other invertebrates, we identified a single SREBP ortholog in Penaeus vannamei (designated PvSREBP) with transcripts ubiquitously expressed in tissues and induced by lipopolysaccharide (LPS), Vibrio parahaemolyticus and Streptococcus iniae. In vivo RNA interference (RNAi) of PvSREBP attenuated the expression of several fatty acid metabolism-related genes (i.e., cyclooxygenase (PvCOX), lipoxygenase (PvLOX), fatty acid binding protein (PvFABP) and fatty acid synthase (PvFASN)), which consequently decreased the levels of total polyunsaturated fatty acids (ΣPUFAs). In addition, PvSREBP silencing decreased transcript levels of several immune-related genes such as hemocyanin (PvHMC) and trypsin (PvTrypsin), as well as genes encoding for heat-shock proteins (i.e., PvHSP60, PvHSP70 and PvHSP90). Moreover, in silico analysis revealed the presence of SREBP binding motifs on the promoters of most of the dysregulated genes, while shrimp depleted of PvSREBP were more susceptible to V. parahaemolyticus infection. Collectively, we demonstrated the involvement of shrimp SREBP in fatty acids metabolism and immune response, and propose that PvSREBP and PvHMC modulate each other through a feedback mechanism to establish homeostasis. The current study is the first to show the dual role of SREBP in fatty acid metabolism and immune response in invertebrates and crustaceans.

microRNA-589-5p modulates the expression of hemocyanin as part of the anti-WSSV immune response in Litopenaeus vannamei

The respiratory glycoprotein, hemocyanin (HMC) has multiple immune-related functions, including antiviral activity. In this study, in silico methods were used to predict seven miRNAs targeting Litopenaeus vannamei HMC (LvHMC), out of which miR-589-5p was selected for further investigation because of its role in immune response. Transcript levels of miR-589-5p were ubiquitously distributed in all shrimp tissues examined, and significantly induced in hemocytes and hepatopancreas upon challenge with white-spot syndrome virus (WSSV) as well as by marine bacterial pathogens, which suggest that miR-589-5p is involved in shrimp immune response to pathogens. Morever, using Drosophila S2 cells stably overexpressing EGFP-LvHMC, flow cytometry and dual luciferase reporter assays, miR-589-5p was shown to significantly inhibit the in vitro expression of LvHMC. In addition, in vivo knockdown of miR-589-5p using antagomir-589-5p resulted in significant down-regulation in LvHMC expression, while overexpression of miR-589-5p using agomir-589-5p decreased the level of LvHMC expression in shrimp hemocytes and hepatopancreas. Further, the increased expression of miR-589-5p resulted in high shrimp mortality following WSSV challenge, coupled with an increase in the number of WSSV copies in hemocytes and hepatopancreas. These results suggest that miR-589-5p is involved in shrimp immune response to WSSV by negatively regulating the expression of LvHMC.

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.

Antiviral Peptides: Identification and Validation

Despite rapid advances in the human healthcare, the infection caused by certain viruses results in high morbidity and mortality accentuate the importance for development of new antivirals. The existing antiviral drugs are limited, due to their inadequate response, increased rate of resistance and several adverse side effects. Therefore, one of the newly emerging field “peptide-based therapeutics” against viruses is being explored and seems promising. Over the last few years, a lot of scientific effort has been made for the identification of novel and potential peptide-based therapeutics using various advanced technologies. Consequently, there are more than 60 approved peptide drugs available for sale in the market of United States, Europe, Japan, and some Asian countries. Moreover, the number of peptide drugs undergoing the clinical trials is rising gradually year by year. The peptide-based antiviral therapeutics have been approved for the Human immunodeficiency virus (HIV), Influenza virus and Hepatitis virus (B and C). This review enlightens the various peptide sources and the different approaches that have contributed to the search of potential antiviral peptides. These include computational approaches, natural and biological sources (library based high throughput screening) for the identification of lead peptide molecules against their target. Further the applications of few advanced techniques based on combinatorial chemistry and molecular biology have been illustrated to measure the binding parameters such as affinity and kinetics of the screened interacting partners. The employment of these advanced techniques can contribute to investigate antiviral peptide therapeutics for emerging infections.

The krüppel-like factor of Penaeus vannamei negatively regulates transcription of the small subunit hemocyanin gene as part of shrimp immune response

Hemocyanin is a multifunctional respiratory glycoprotein, which has also been implicated in other biological functions in shrimp. Moreover, recent studies have revealed that hemocyanin is also involved in a broad range of immune-related activities in shrimp. However, in spite of the considerable interest in unraveling the reasons behind the multiple immune-related functions of hemocyanin, little is known about its transcriptional regulation. Here, DNA pull-down and Liquid Chromatography - Tandem Mass Spectrometry (LC-MS/MS) analyses were used to isolate and identify the putative transcription factor(s) that are involved in the transcriptional regulation of the small subunit hemocyanin gene of Penaeus vannamei (PvHMCs). Krüppel-like factor (designated PvKruppel), a zinc finger transcription factor homolog in P. vannamei, was identified among the putative transcription factors, while bioinformatics analysis revealed the presence of Krüppel-like factor binding site (KLF motif) on the core promoter region of PvHMCs. Mutational analysis and electrophoretic mobility shift assay (EMSA) confirmed that PvKruppel could bind to the KLF motif on the core promoter region of PvHMCs. Moreover, in response to lipopolysaccharide (LPS), Vibrio parahaemolyticus and white spot syndrome virus (WSSV) challenge, transcript levels of PvKruppel and PvHMCs were negatively correlated. Furthermore, overexpression of PvKruppel significantly reduced the promoter activity of PvHMCs, while PvKruppel knockdown by RNA interference or lipopolysaccharides (LPS) stimulation resulted in a significant increase in the transcript level of PvHMCs. Taken together, our present study provides mechanistic insights into the transcriptional regulation of PvHMCs by PvKruppel during shrimp immune response to pathogens.

A comparative synthesis of transcriptomic analyses reveals major differences between WSSV-susceptible Litopenaeus vannamei and WSSV-refractory Macrobrachium rosenbergii

Since the 1990s White Spot Syndrome Virus (WSSV) has severely affected shrimp aquaculture worldwide causing a global pandemic of White Spot Disease (WSD) in penaeid culture. However, not all decapod species that can be infected by WSSV show the same susceptibility to the virus, thus raising interesting questions regarding the potential genetic traits that might confer resistance to WSSV. In order to shed light into the genetic markers of WSSV resistance, we employed a dual approach: i) we initially analysed the transcriptomes derived from the hepatopancreas of two species, the susceptible white shrimp Litopenaeus vannamei and the refractory fresh water prawn Macrobrachium rosenbergii, both infected with WSSV. We found a large number of differentially expressed genes (DEGs) belonging to the immune system (mostly anti-microbial peptides and haemolymph clotting components) that were generally up-regulated in M. rosenbergii and down-regulated in L. vannamei. Further, in both species we identified many up-regulated DEGs that were related to metabolism (suggesting a metabolic shift during the infection) and, interestingly, in L. vannamei only, we found several DEGs that were related to moult and suggested an inhibition of the moult cycle in this species following WSSV infection. ii) we then identified a limited number of genetic markers putatively linked with WSD tolerance by employing an ecological genomics approach in which we compared published reports with our own RNA-seq datasets for different decapod species infected with WSSV. Using this second comparative approach, we found nine candidate genes which are consistently down-regulated in susceptible species and up-regulated in refractory species and which have a role in immune response. Together our data offer novel insights into gene expression differences that can be found in susceptible and refractory decapod species infected with WSSV and provide a valuable resource towards our understanding of the potential genetic basis of tolerance to WSSV.

Resolving hemocyanin isoform complexity in haemolymph of black tiger shrimp Penaeus monodon - implications in aquaculture, medicine and food safety

Hemocyanin (Hc) is a multifunctional macromolecule involved in oxygen transport and non-specific immunity in shrimp. Hc is crucial in physiology and nutrition linked with optimal performance in aquaculture production systems. In medicine, Hc has been approved for clinical use in humans as adjuvant and anticancer therapeutic. In contrast, Hc has also been identified as one of the proteins causing anaphylaxis following shrimp consumption. The role of individual Hc isoforms remains unknown due to a lack of resolved Hc isoforms. We successfully identified eleven different Penaeus monodon hemocyanin (PmoHc) γ isoforms including two truncated isoforms (50 and 20 kDa) and one PmoHc β isoform in haemolymph using proteomics informed by transcriptomics. Amino acid sequence homology ranged from 24 to 97% between putative PmoHc gene isoforms. Hc isoforms showed specific patterns of transcript expression in shrimp larval stages and adult hepatopancreas. These findings enable isoform level investigations aiming to define molecular mechanisms underpinning Hc functionality in shrimp physiology and immunity, as well as their individual immunogenic role in human allergy. Our research demonstrates the power of proteomics informed by transcriptomics to resolve isoform complexity in non-model organisms and lay the foundations for improved performance within the aquaculture industry and advance allergenic applications in medicine. SIGNIFICANCE: The roles of hemocyanin (Hc) in shrimp homeostasis and immunity as well as in human allergy are not well understood because the complexity of Hc isoforms has remained unresolved. Our results have confirmed the existence of at least 12 individual Hc isoforms in shrimp haemolymph and validated putative Hc gene assemblies from transcriptomics. Our findings will enable monitoring the expression of specific Hc isoforms in shrimp haemolymph during different environmental, nutritional and pathogenic conditions, thus providing insights into isoform specific functional roles. In medicine, the potential allergenicity of each Hc isoform could be determined and advance allergenic applications. Lastly, since Hc comprises up to 95% of the total protein in haemolymph, these isoforms become ideal targets for prawn provenance, traceability and food contamination studies.

Multifunctional Roles of Hemocyanins

The copper-containing hemocyanins are proteins responsible for the binding, transportation and storage of dioxygen within the blood (hemolymph) of many invertebrates. Several additional functions have been attributed to both arthropod and molluscan hemocyanins, including (but not limited to) enzymatic activity (namely phenoloxidase), hormone transport, homeostasis (ecdysis) and hemostasis (clot formation). An important secondary function of hemocyanin involves aspects of innate immunity-such as acting as a precursor of broad-spectrum antimicrobial peptides and microbial/viral agglutination. In this chapter, we present the reader with an up-to-date synthesis of the known functions of hemocyanins and the structural features that facilitate such activities.

Comparative analysis of shrimp (Penaeus vannamei) miRNAs expression profiles during WSSV infection under experimental conditions and in pond culture

In recent years, the importance of viral and host microRNAs (miRNAs) in mediating viral replication and control of host cellular machinery, has been realised and increasing efforts have been taken in order to understand the interactions of miRNAs from host and pathogen during infection. However, all existing studies has thus far been conducted in controlled experimental conditions and the veracity of these data for field conditions are yet to be established. In this framework, small RNA sequencing was performed to identify the miRNAs involved in shrimp (Penaeus vannamei) immune responses under two different WSSV infection conditions of natural infection and experimentally challenged conditions. The expression profiles of miRNAs of shrimp infected with WSSV under two contrasting conditions were compared and as a result, 23365 known miRNAs and 481 novel miRNAs were identified. Amongst the most abundantly expressed miRNAs, the hypoxia related miR-210 and immune pathway related miR-29b were expressed only in infected shrimps of both conditions. miR-8-5p, having a functional role in modulation of chitin biosynthesis was exclusively represented in higher numbers in the WSSV -infected shrimps under natural conditions whilst four of the miRNAs (mja-miR-6493-5p, mja-miR-6492, mmu-miR-3968, tcf-miR-9b-5p) identified from shrimps collected from pond culture targeted chitinase, an important enzyme involved in growth and moulting in shrimps, indicating an interaction between WSSV infection and moult cycle under culture conditions. Some of the miRNAs (tca-miR-87b-3p, cte-miR-277a) and miRNAs belonging to class miR-9, miR-981 that were identified only in WSSV infected shrimps under experimental conditions, are known to respond against WSSV infection in shrimps. Moreover, the miRNA target prediction revealed several immune-related gene targets such as cathepsin, c-type lectin, haemocyanin and ubiquitin protein ligase were commonly identified under both the conditions. However, the miRNAs identified from challenge experiment had wide number of gene targets as compared to the miRNAs of natural infection. The shrimp miRNA mja-miR-6489-3p, was also found to target early virus gene wsv001 of WSSV. Our study, therefore, provides the comparative analysis of miRNA expression from shrimp during WSSV infection in two different conditions.

Litopenaeus vannamei Src64B restricts white spot syndrome virus replication by modulating apoptosis

The Src family kinases (SFK) are involved in signaling transductions that regulate numerous biological activities including host-virus interaction. These features of SFK have been well explored in vertebrates, however, in shrimp, the invertebrate SFK family member Src64B, has not been characterized and therefore its role in shrimp-virus interaction remains unknown. In this study, two Litopenaeus vannamei Src64B isoforms (designated LvSrc64B1 and LvSrc64B2) were first cloned and their role in white spot syndrome virus (WSSV) infection was explored. Bioinformatics analysis revealed that LvSrc64B1 and LvSrc64B2 were similar to other Src64B family members, with high homology in primary and tertiary structures, and contained the conserved SFK functional domains, as well as the putative myristylation and phosphorylation sites. Tissue distribution analysis showed that both LvSrc64B isoforms were ubiquitously expressed, albeit distinctively in the tested tissues. In addition, transcript levels of LvSrc64B1 and LvSrc64B2 were significantly induced following WSSV challenge and had similar expression patterns. Furthermore, siRNA-mediated knockdown of LvSrc64B1 and LvSrc64B2 followed by WSSV infection resulted in increased expression of viral genes, enhanced viral DNA replication, and elevation of hemocytes apoptosis. Depletion of LvSrc64B1 and LvSrc64B2 also reduced shrimp survival upon WSSV infection. In conclusion, the current data strongly suggest that Src64B is a host factor that inhibits WSSV replication by modulating apoptosis in shrimp.

Computational identification of self-inhibitory peptides from white spot syndrome virus envelope protein VP28

Since effective chemotherapeutics or preventive measures are still unavailable, finding feasible approaches against white spot syndrome virus (WSSV) has always been the vital subject in shrimp farming field. Envelope proteins are the ideal targets for antiviral strategies development due to their indispensable roles in virus entry, and inhibitory peptides targeting them have been proved to be promising in blocking virus infection. In this study, the Wimley-White interfacial hydrophobicity scale (WWIHS) in combination with known structural data was applied to identify potential inhibitory peptides that targeted the envelope protein VP28 of WSSV. Results showed that two potential inhibitory peptides were identified, one of which exhibited not only obvious antiviral activity, but also broad-spectrum antimicrobial activity. The inhibitory peptide identified here can serve as a lead compound for anti-WSSV strategies development.