In vivo activity and the transcriptional regulatory mechanism of the antimicrobial peptide SpHyastatin in Scylla paramamosain

Expression of BSN314 lysozyme genes in Escherichia coli BL21: a study to demonstrate microbicidal and disintegarting potential of the cloned lysozyme

This study is an extension of our previous studies in which the lysozyme was isolated and purified from Bacillus subtilis BSN314 (Naveed et al., 2022; Naveed et al., 2023). In this study, the lysozyme genes were cloned into the E. coli BL21. For the expression of lysozyme in E. coli BL21, two target genes, Lyz-1 and Lyz-2, were ligated into the modified vector pET28a to generate pET28a-Lyz1 and pET28a-Lyz2, respectively. To increase the production rate of the enzyme, 0.5-mM concentration of IPTG was added to the culture media and incubated at 37 °C and 220 rpm for 24 h. Lyz1 was identified as N-acetylmuramoyl-L-alanine amidase and Lyz2 as D-alanyl-D-alanine carboxypeptidase. They were purified by multi-step methodology (ammonium sulfate, precipitation, dialysis, and ultrafiltration), and antimicrobial activity was determined. For Lyz1, the lowest MIC/MBC (0.25 μg/mL; with highest ZOI = 22 mm) were recorded against Micrococcus luteus, whereas the highest MIC/MBC with lowest ZOI were measured against Salmonella typhimurium (2.50 μg /mL; with ZOI = 10 mm). As compared with Aspergillus oryzae (MIC/MFC; 3.00 μg/mL), a higher concentration of lysozyme was required to control the growth of Saccharomyces cerevisiae (MIC/MFC; 50 μg/mL). Atomic force microscopy (AFM) was used to analyze the disintegrating effect of Lyz1 on the cells of selected Gram-positive bacteria, Gram-negative bacteria, and yeast. The AFM results showed that, as compared to Gram-negative bacteria, a lower concentration of lysozyme (Lyz1) was required to disintegrate the cell of Gram-positive bacteria.

A Novel Antimicrobial Peptide Spampcin56-86 from Scylla paramamosain Exerting Rapid Bactericidal and Anti-Biofilm Activity In Vitro and Anti-Infection In Vivo

The abuse of antibiotics leads to the increase of bacterial resistance, which seriously threatens human health. Therefore, there is an urgent need to find effective alternatives to antibiotics, and antimicrobial peptides (AMPs) are the most promising antibacterial agents and have received extensive attention. In this study, a novel potential AMP was identified from the marine invertebrate Scylla paramamosain and named Spampcin. After bioinformatics analysis and AMP database prediction, four truncated peptides (Spa31, Spa22, Spa20 and Spa14) derived from Spampcin were screened, all of which showed potent antimicrobial activity with different antibacterial spectrum. Among them, Spampcin_56-86 (Spa31 for short) exhibited strong bactericidal activity against a variety of clinical pathogens and could rapidly kill the tested bacteria within minutes. Further analysis of the antibacterial mechanism revealed that Spa31 disrupted the integrity of the bacterial membrane (as confirmed by scanning electron microscopy observation, NPN, and PI staining assays), leading to bacterial rupture, leakage of cellular contents (such as elevated extracellular ATP), increased ROS production, and ultimately cell death. Furthermore, Spa31 was found to interact with LPS and effectively inhibit bacterial biofilms. The antibacterial activity of Spa31 had good thermal stability, certain ion tolerance, and no obvious cytotoxicity. It is worth noting that Spa31 could significantly improve the survival rate of zebrafish Danio rerio infected with Pseudomonas aeruginosa, indicating that Spa31 played an important role in anti-infection in vivo. This study will enrich the database of marine animal AMPs and provide theoretical reference and scientific basis for the application of marine AMPs in medical fields.

A Novel Antimicrobial Peptide Sparanegtin Identified in Scylla paramamosain Showing Antimicrobial Activity and Immunoprotective Role In Vitro and Vivo

The abuse of antibiotics in aquaculture and livestock no doubt has exacerbated the increase in antibiotic-resistant bacteria, which imposes serious threats to animal and human health. The exploration of substitutes for antibiotics from marine animals has become a promising area of research, and antimicrobial peptides (AMPs) are worth investigating and considering as potential alternatives to antibiotics. In the study, we identified a novel AMP gene from the mud crab Scylla paramamosain and named it Sparanegtin. Sparanegtin transcripts were most abundant in the testis of male crabs and significantly expressed with the challenge of lipopolysaccharide (LPS) or Vibrio alginolyticus. The recombinant Sparanegtin (rSparanegtin) was expressed in Escherichia coli and purified. rSparanegtin exhibited activity against Gram-positive and Gram-negative bacteria and had potent binding affinity with several polysaccharides. In addition, rSparanegtin exerted damaging activity on the cell walls and surfaces of P. aeruginosa with rougher and fragmented appearance. Interestingly, although rSparanegtin did not show activity against V. alginolyticus in vitro, it played an immunoprotective role in S. paramamosain and exerted an immunomodulatory effect by modulating several immune-related genes against V. alginolyticus infection through significantly reducing the bacterial load in the gills and hepatopancreas and increasing the survival rate of crabs.

Characterization and antimicrobial evaluation of a new Spgly-AMP, glycine-rich antimicrobial peptide from the mud crab Scylla paramamosain

Antimicrobial peptide (AMP) is a crucial component of the innate immune system in crustaceans. In mud crab, Scylla paramamosain, a commercially important species, a glycine-rich antimicrobial peptide (Spgly-AMP) gene was newly identified and putatively encoded a 26aa signal peptide and 37aa mature peptide. To understand the function of Spgly-AMP, the expression profile of Spgly-amp gene was characterized, which showed Spgly-amp was expressed widely in most tissues of adult crabs with the highest expression level in hemocytes. After Vibrio parahaemolyticus, PGN, or Poly I:C stimulations, the expression level of Spgly-amp was significantly up-regulated in the hemocytes. In antimicrobial assays, chemically synthesized Spgly-AMP peptides exhibited strong antibacterial activities against both Gram-positive and Gram-negative bacteria and high thermal stability after high-temperature heating. These findings in the present study verified the importance of the Spgly-AMP in defense of pathogenic bacteria infection in the mud crab and provided a promising candidate of antimicrobial agents in the crab aquaculture.

Hepatopancreas immune response during molt cycle in the mud crab, Scylla paramamosain

Molt is a critical developmental process in crustaceans. Recent studies have shown that the hepatopancreas is an important source of innate immune molecules, yet hepatopancreatic patterns of gene expression during the molt cycle which may underlie changes in immune mechanism are unknown. In this study, we performed Illumina sequencing for the hepatopancreas of the mud crab, Scylla paramamosain during molt cycle (pre-molt stage, post-molt stage, and inter-molt stage). A total of 44.55 Gb high-quality reads were obtained from the normalized cDNA of hepatopancreas. A total of 70,591 transcripts were assembled; 55,167 unigenes were identified. Transcriptomic comparison revealed 948 differentially expressed genes (DEGs) in the hepatopancreas from the three molt stages. We found that genes associated with immune response patterns changed in expression during the molt cycle. Antimicrobial peptide genes, inflammatory response genes, Toll signaling pathway factors, the phenoloxidase system, antioxidant enzymes, metal-binding proteins and other immune related genes are significantly up-regulated at the post-molt stage and inter-molt stage compared with the pre-molt stage, respectively. These genes are either not expressed or are expressed at low levels at the pre-molt stage. To our knowledge, this is the first systematic transcriptome analysis of genes capable of mobilizing a hepatopancreas immune response during the molt cycle in crustaceans, and this study will contribute to a better understanding of the hepatopancreas immune system and mud crab prophylactic immune mechanisms at the post-molt stage.

The NF-κB family member dorsal plays a role in immune response against Gram-positive bacterial infection in mud crab (Scylla paramamosain)

The NF-κB family is a set of evolutionarily conserved transcription factors that play central roles in various biological events. Dorsal is an invertebrate NF-κB family member that is essential for the regulation of immune responses. In the current study, the Dorsal gene from Scylla paramamosain (SpDorsal) was identified, which showed high homology to other crustacean Dorsal proteins. Expression of SpDorsal was highest in hemocytes and could be significantly changed after immune stimulations. In expression vector-transfected S2 cells, SpDorsal was mainly localized in the cytoplasm and could be efficiently translocated into the nucleus upon immune stimulations with the Gram-positive bacteria Staphylococcus aureus and poly (I:C), but not the Gram-negative bacteria Vibrio parahaemolyticus. As a transcription factor, SpDorsal could activate the promoter of S. paramamosain Hyastatin (SpHyastatin) in vitro, while S. paramamosain Cactus (SpCactus), a homolog of IκB, could interact with SpDorsal to prevent its nuclear translocation and inhibit its transcription factor activity. Silencing of SpDorsal in vivo using RNAi strategy significantly increased the mortality of crabs infected with S. aureus but not that with V. parahaemolyticus. These indicated that the SpDorsal signaling pathway could be mainly implicated in immune responses against Gram-positive bacterial infection in S. paramamosain.

Pattern recognition receptors and their roles on the innate immune system of mud crab (Scylla paramamosain)

The innate immune system is the first line of defense protecting the hosts against invading pathogens. Mud crab (Scylla paramamosain) is widely distributed in China and Indo-west Pacific countries, which develops a very complicated innate immune system against pathogen invasions. Innate immunity involves the humoral and cellular responses that are linked to the pattern recognition receptors (PRRs). PRRs initially recognize the infection and trigger the activation of signaling cascades, leading to transcriptional regulation of inflammatory mediators that function in pathogenic control and clearance. In mud crab S. paramamosain, the Toll/Toll-like receptors, lipopolysaccharide and β-1,3-glucan binding proteins, C-type lectins, scavenger receptors, and down syndrome cell adhesion molecules have been identified as receptor families responsible for the recognition of bacteria, fungi, and viruses, and are important components in the innate immune system. In this review, we summarize the literature on the current knowledge and the roles of PRRs in the immune defenses of mud crab, which in an effort to provide much information for further researches.

Characterization of the innate immunity in the mud crab Scylla paramamosain

Mud crabs, Scylla paramamosain, are one of the most economical and nutritious crab species in China and South Asia. Inconsistent with the high development of commercial mud crab aquaculture, effective immunological methods to prevent frequently-occurring diseases have not yet been developed. Thus, high mortalities often occur throughout the different developmental stages of this species resulting in large economic losses. In recent years, numerous attempts have been made to use various advanced biological technologies to understand the innate immunity of S. paramamosain as well as to characterize specific immune components. This review summarizes these research advances regarding cellular and humoral responses of the mud crab during pathogen infection, highlighting hemocytes and gills defense, pattern recognition, immune-related signaling pathways (Toll, IMD, JAK/STAT, and prophenoloxidase (proPO) cascades), immune effectors (antimicrobial peptides), production of reactive oxygen species and the antioxidant system. Diseases affecting the development of mud crab aquaculture and potential disease control strategies are discussed.

Molecular characterization, expression and antimicrobial activities of a c-type lysozyme from the mud crab, Scylla paramamosain

Lysozyme is an important immune protein involved in the first line of defense for crustaceans. In the present study, a c-type lysozyme gene (SpLyzC) was cloned and characterized from the mud crab, Scylla paramamosain. The full-length cDNA was 849 bp with an open reading frame of 669 bp, and encoded a polypeptide of 223 amino acids with a calculated molecular mass of 23.7 kDa and an isoelectric point of 8.90. SpLyzC shared conserved active sites with c-type lysozymes from other species, detected in all tested tissues and had higher expression levels in hepatopancreas and gill tissues. The expression of SpLyzC was up-regulated in hepatopancreas and gill after infection with Vibrio parahaemolyticus and Staphylococcus aureus. The density of bacteria in the hemolymph and the mortality of crabs increased following infection with V. parahaemolyticus after SpLyzC expression was silenced by injecting double-strand RNA of SpLyzC. The recombinant protein of the S. paramamosain c-type lysozyme (rSpLyzC) exhibited antibacterial activities against Micrococcus lysodeikticus, S. aureus, Vibrio harveyi and V. parahaemolyticus. These results indicate that SpLyzC could help eliminate bacteria in S. paramamosain and may play an important role in resistance to bacterial infection.

Peptides as epigenetic modulators: therapeutic implications

Peptides originating from different sources (endogenous, food derived, environmental, and synthetic) are able to influence different aspects of epigenetic regulation. Endogenous short peptides, resulting from proteolytic cleavage of proteins or upon translation of non-annotated out of frame transcripts, can block DNA methylation and hereby regulate gene expression. Peptides entering the body by digestion of food-related proteins can modulate DNA methylation and/or histone acetylation while environmental peptides, synthesized by bacteria, fungi, and marine sponges, mainly inhibit histone deacetylation. In addition, synthetic peptides that reverse or inhibit different epigenetic modifications of both histones and the DNA can be developed as well. Next to these DNA and histone modifications, peptides can also influence the expression of non-coding RNAs such as lncRNAs and the maturation of miRNAs.

Seen the advantages over small molecules, the development of peptide therapeutics is an interesting approach to treat diseases with a strong epigenetic basis like cancer and Alzheimer’s disease. To date, only a limited number of drugs with a proven epigenetic mechanism of action have been approved by the FDA of which two (romidepsin and nesiritide) are peptides. A large knowledge gap concerning epigenetic effects of peptides is present, and this class of molecules deserves more attention in the development as epigenetic modulators. In addition, none of the currently approved peptide drugs are under investigation for their potential effects on epigenetics, hampering drug repositioning of these peptides to other indications with an epigenetic etiology.

SpToll1 and SpToll2 modulate the expression of antimicrobial peptides in Scylla paramamosain

Tolls and Toll-like receptors (TLRs) were the first pattern recognition receptors (PRRs) identified to play key roles in host innate immunity. However, relatively little is known about other types of Toll-like receptors in Scylla paramamosain, although a Toll-like receptor (SpToll1) has recently been cloned. In this study, we cloned and characterized another novel Toll-like receptor 2 (SpToll2) from S. paramamosain. The full-length cDNA of SpToll2 is 3391 bp with a 2646 bp open reading frame (ORF) encoding a putative protein of 881 amino acids, and predicted to contain six extracellular leucine-rich repeat (LRR) domains, a transmembrane domain and an intracellular Toll/IL-1 receptor (TIR) domain. Phylogenetic analysis revealed that SpToll2 clustered with Drosophila Toll1, and shared high homology with PtToll4. Real-time qPCR analysis showed that SpToll2 was widely expressed in all tissues tested, with the highest level found in hemocytes and hepatopancreas while the lowest in heart and muscle. The transcript levels of both SpToll1 and SpToll2 in mud crabs hemocytes was induced following challenge with Vibrio parahaemolyticus, Staphylococcus aureus, Polyinosinic: polycytidylic acid (Poly I:C) and white spot syndrome virus (WSSV). In addition, recombinant SpToll1-LRR and SpToll2-LRR proteins could bind to V. parahaemolyticus, S. aureus, Escherichia coli, and Beta Streptococcus. In order to study the signaling pathway of AMPs' expression in mud crab, RNA interference were used to test the expression of SpAMPs after the challenges with V. parahaemolyticus or S. aureus. The data suggested that SpToll1and SpToll2 could regulate the transcripts of several AMPs and four immune related mediators (SpMyD88, SpTube, SpPelle and SpTRAF6) at different scale. While silencing of SpToll1 post pathogens challenge attenuated the expression of SpHistin, SpALF1 and SpALF5 in mud crab's hemocytes, depletion of SpToll2 post pathogens challenge inhibited the expression of SpALF1-6, SpGRP, SpArasin and SpHyastastin. Furthermore, the results of overexpression assay also showed SpToll1 and SpToll2 could enhance the promoter activities of SpALFs in mud crab. Taken together, these results indicated that SpToll1 and SpToll2 might play important roles in host defense against pathogen invasions in S. paramamosain.

Characterization and antimicrobial evaluation of SpPR-AMP1, a proline-rich antimicrobial peptide from the mud crab Scylla paramamosain

Antimicrobial peptide (AMP) is an important molecule in the innate immune system. Here, we report the cloning and functional studies of proline-rich AMPs (PR-AMPs) from the three species of mud crab: Scylla paramamosain, S. serrata, and the swimming crab Portunus pelagicus. The deduced peptides revealed that they contain the putative signal peptides and encode for mature peptides, which contain sequence architecture similar to a 6.5-kDa proline-rich AMP of the shore crab, Carcinus maenas which showed similarity with the bactenecin7. Tissue distribution analysis indicated that the SpPR-AMP1 was expressed in a wide range of adult tissues, with the highest expression levels in the crab hemocyte. Challenge experiments showed that the levels of SpPR-AMP1 mRNA expression were up-regulated in the hemocyte after peptidoglycan stimulation. To evaluate the biological properties of mature SpPR-AMP1, peptides were chemically synthesized and recombinantly expressed. SpPR-AMP1 showed strong antibacterial activity against both Gram-positive bacteria Micrococcus luteus and Gram-negative bacteria Vibrio harveyi. The results indicate that the SpPR-AMP1 plays a role in crab immunity.

H2A and Ca-L-hipposin gene: Characteristic analysis and expression responses to Aeromonas hydrophila infection in Carassius aurutus

Antimicrobial peptide is an important component of the host innate immune system and thus serves a crucial function in host defense against microbial invasion. In this study, H2A and derived antimicrobial peptide Ca-L-hipposin were cloned and characterized in Carassius aurutus. The gene H2A full-length cDNA is 908 bp and includes a 5'-terminal untranslated region (UTR) of 55 bp and a 3'-terminal UTR of 466 bp with a canonical polyadenylation signal sequence AATAA, as well as an open reading frame (ORF) of 387 bp encoding a polypeptide of 128 amino acids, with a molecular weight of 13.7 kDa, an isoelectric point of 10.7, and 94% homology with Danio rerio H2A. The secondary structure of H2A includes the α-spiral with 51 amino acids with a composition ratio of 39.8%, as well as a β-corner with 15 amino acids in a composition ratio of 11.7%. The online software ExPaSy predicted that a peptide sequence with 51 amino acids from the 2nd to 52nd amino acids in histone H2A can be produced through hydrolization by protease chymotrypsin, which indicates a difference of only three amino acids, compared with the antimicrobial peptide hipposin in Hippoglossus hippoglossus with a homology of 94%. Ca-L-hipposin includes 51 amino acids with a molecular weight of 5.4 kDa and an isoelectric point of 12.0, the secondary structure of which contains an α-helix of 17 amino acids accounting for 33.3% and a β-corner of 8 amino acids accounting for 15.7%. H2A was extensively expressed in the mRNA levels of various tissues, with higher expression levels in kidney and spleen. After C. aurutus was challenged with Aeromonas hydrophila, the mRNA expression levels of H2A were upregulated in the kidney, spleen, and liver. H2A serves an important function in the defense against the invasion of A. hydrophila. In addition, sequence characteristics reveal that Ca-L-hipposin could be a potential antimicrobial peptide for use in killing pathogenic bacteria in aquaculture.