Defensin like peptide from Panulirus argus relates structurally with beta defensin from vertebrates

Improving the antimicrobial potential of the peptide CIDEM-501 through acylation: A computational approach

Acylation is a common method used to modify antimicrobial peptides to enhance their effectiveness. It increases the interactions between the peptide and the bacterial cell membranes. However, acylation can also reduce the selectivity of the peptides by making them more active on eukaryotic membranes, which can lead to unintended toxicity. This study examines the potential of using in silico tools to evaluate the interaction and selectivity of the antimicrobial peptide CIDEM-501 when acylated with decanoic acid at the N-terminus, compared to the non-acylated counterpart. Circular dichroism, microdilution, and hemolysis assays were used to determine the peptide's secondary structure, antimicrobial activity, and selectivity to validate the theoretical predictions. The acylated peptide showed a more stable interaction with the bacterial membrane by inserting the acyl chain into the membrane's hydrophobic core, which led to tighter adsorption and a greater buried surface area. Additionally, it significantly altered membrane order more than the non-acylated counterpart, suggesting superior antimicrobial potential. Finally, in vitro activity assays confirmed theoretical predictions, showing that the acylated peptide had lower Minimum Inhibitory Concentration (MIC) values than the non-acylated peptide. Neither peptide showed significant hemolytic activity at their MIC. The computational techniques used in this study displayed strong predictive capability and helped to elucidate the interaction between the peptide and the membranes.

A Novel Beta-Defensin Isoform from Malabar Trevally, Carangoides malabaricus (Bloch & Schneider, 1801), an Arsenal Against Fish Bacterial Pathogens: Molecular Characterization, Recombinant Production, and Mechanism of Action

Antimicrobial peptides (AMPs), including beta-defensin from fish, are a crucial class of peptide medicines. The focus of the current study is the molecular and functional attributes of CmDef, a 63-amino acid beta-defensin AMP from Malabar trevally, Carangoides malabaricus. This peptide demonstrated typical characteristics of AMPs, including hydrophobicity, amphipathic nature, and +2.8 net charge. The CmDef was recombinantly expressed and the recombinant peptide, rCmDef displayed a strong antimicrobial activity against bacterial fish pathogens with an MIC of 8 µM for V. proteolyticus and 32 µM for A. hydrophila. The E. tarda and V. harveyi showed an inhibition of 94% and 54%, respectively, at 32 µM concentration. No activity was observed against V. fluvialis and V. alginolyticus. The rCmDef has a multimode of action that exerts an antibacterial effect by membrane depolarization followed by membrane permeabilization and ROS production. rCmDef also exhibited anti-cancer activities in silico without causing hemolysis. The peptide demonstrated stability under various conditions, including different pH levels, temperatures, salts, and metal ions (KCl and CaCl2), and remained stable in the presence of proteases such as trypsin and proteinase K at concentrations up to 0.2 µg/100 µl. The strong antibacterial efficacy and non-cytotoxic nature suggest that rCmDef is a single-edged sword that can contribute significantly to aquaculture disease management.

Antibacterial Efficacy and Mechanisms of Action of a Novel Beta-Defensin from Snakehead Murrel, Channa striata

Beta-defensins, identified from fishes, constitute a crucial category of antimicrobial peptides important in combating bacterial fish pathogens. The present investigation centers on the molecular and functional characterization of CsDef, a 63-amino acid beta-defensin antimicrobial peptide derived from snakehead murrel (Channa striata). The physicochemical attributes of CsDef align with the distinctive characteristics observed in AMPs. CsDef was recombinantly produced, and the recombinant peptide, rCsDef, exhibited notable antibacterial efficacy against bacterial fish pathogens with an MIC of 16 μM for V. proteolyticus. A. hydrophila exhibited 91% inhibition, E. tarda 92%, and V. harveyi 53% at 32 μM of rCsDef. The rCsDef exhibited a multifaceted mechanism of action against bacteria, i.e., through membrane depolarization, membrane permeabilization, and generation of ROS. The rCsDef was non-hemolytic to hRBCs and non-cytotoxic to normal mammalian cell line CHO-K1. However, it exhibited anticancer properties in MCF-7. rCsDef demonstrated notable stability with respect to pH, temperature, salt, metal ions, and proteases. These findings suggest it is a potential candidate molecule for prospective applications in aquaculture.

Marine Antimicrobial Peptides: An Emerging Nightmare to the Life-Threatening Pathogens

The emergence of multidrug-resistant pathogens due to improper usage of conventional antibiotics has created a global health crisis. Alternatives to antibiotics being an urgent need, the scientific community is forced to search for new antimicrobials. This exploration has led to the discovery of antimicrobial peptides, a group of small peptides occurring in different phyla such as Porifera, Cnidaria, Annelida, Arthropoda, Mollusca, Echinodermata, and Chordata, as a component of their innate immune system. The marine environment, possessing immense diversity of organisms, is undoubtedly one of the richest sources of unique potential antimicrobial peptides. The distinctiveness of marine antimicrobial peptides lies in their broad-spectrum activity, mechanism of action, less cytotoxicity, and high stability, which form the benchmark for developing a potential therapeutic. This review aims to (1) synthesise the available information on the distinctive antimicrobial peptides discovered from marine organisms, particularly over the last decade, and (2) discuss the distinctiveness of marine antimicrobial peptides and their prospects.

Insights into the Adsorption Mechanisms of the Antimicrobial Peptide CIDEM-501 on Membrane Models

CIDEM-501 is a hybrid antimicrobial peptide rationally designed based on the structure of panusin and panulirin template peptides. The new peptide exhibits significant antibacterial activity against multidrug-resistant pathogens (MIC = 2-4 μM) while conserving no toxicity in human cell lines. We conducted molecular dynamics (MD) simulations using the CHARMM-36 force field to explore the CIDEM-501 adsorption mechanism with different membrane compositions. Several parameters that characterize these interactions were analyzed to elucidate individual residues' structural and thermodynamic contributions. The membrane models were constructed using CHARMM-GUI, mimicking the bacterial and eukaryotic phospholipid compositions. Molecular dynamics simulations were conducted over 500 ns, showing rapid and highly stable peptide adsorption to bacterial lipids components rather than the zwitterionic eucaryotic model membrane. A predominant peptide orientation was observed in all models dominated by an electric dipole. The peptide remained parallel to the membrane surface with the center loop oriented to the lipids. Our findings shed light on the antibacterial activity of CIDEM-501 on bacterial membranes and yield insights valuable for designing potent antimicrobial peptides targeting multi- and extreme drug-resistant bacteria.

Antimicrobial Peptides: An Update on Classifications and Databases

Antimicrobial peptides (AMPs) are distributed across all kingdoms of life and are an indispensable component of host defenses. They consist of predominantly short cationic peptides with a wide variety of structures and targets. Given the ever-emerging resistance of various pathogens to existing antimicrobial therapies, AMPs have recently attracted extensive interest as potential therapeutic agents. As the discovery of new AMPs has increased, many databases specializing in AMPs have been developed to collect both fundamental and pharmacological information. In this review, we summarize the sources, structures, modes of action, and classifications of AMPs. Additionally, we examine current AMP databases, compare valuable computational tools used to predict antimicrobial activity and mechanisms of action, and highlight new machine learning approaches that can be employed to improve AMP activity to combat global antimicrobial resistance.

β-Defensins from common goby (Pomatoschistus microps) and silver trevally (Pseudocaranx georgianus): Molecular characterization and phylogenetic analysis

Antimicrobial peptides (AMPs) are biologically active molecules involved in host defense present in a variety of organisms. They are an integral component of innate immunity, forming a front line of defense against potential pathogens, including antibiotic-resistant ones. Fishes are proven to be a prospective source of AMPs as they are constantly being challenged by a variety of pathogens and the AMPs are reported to play an inevitable role in fish immunity. Among them, β-defensins form one of the most studied multifunctional peptides with early evolutionary history and recently being considered as host defense peptides. The present study highlights the first-ever report on β-defensin AMP sequences from common goby (Pomatoschistus microps) and silver trevally (Pseudocaranx georgianus). A 192 bp cDNA fragment with an open reading frame encoding 63 amino acids (aa) comprising a 20 aa signal peptide region at the N-terminal was obtained from the mRNA of gill tissue of both P. microps and P. georgianus by RT-PCR. These peptide sequences when characterized in silico at the molecular level revealed a 43 aa cationic mature peptide with the signature intra-molecular disulphide bonded cysteine residue pattern ascertaining its β-defensin identity, further confirmed by phylogenetic analysis. The data collected will pave the way for further research on varied facets of the peptide-like, tissue level expressions, antimicrobial activities on commonly encountered pathogens, and its feasibility as a therapeutant in the aquaculture scenario.

Utilization of a recombinant defensin from Maize (Zea mays L.) as a potential antimicrobial peptide

The search for effective and bioactive antimicrobial molecules to  encounter the medical need for new antibiotics is an encouraging area of research. Plant defensins are small cationic, cysteine-rich peptides with a stabilized tertiary structure by disulfide-bridges and characterized by a wide range of biological functions. The heterologous expression of Egyptian maize defensin (MzDef) in Escherichia coli and subsequent purification by glutathione affinity chromatography yielded 2 mg/L of recombinant defensin peptide. The glutathione-S-transferase (GST)-tagged MzDef of approximately 30 kDa in size (26 KDa GST +  ~ 4 KDa MzDef peptide) was immunodetected with anti-GST antibodies. The GST-tag was successfully cleaved from the MzDef peptide by thrombin, and the removal was validated by the Tris-Tricine gel electrophoresis. The MzDef induced strong growth inhibition of Rhizoctonia solani, Fusarium verticillioides, and Aspergillus niger by 94.23%, 93.34%, and 86.25%, respectively, whereas relatively weak growth inhibitory activity of 35.42% against Fusarium solani was recorded. Moreover, strong antibacterial activities were demonstrated against E. coli and Bacillus cereus and the moderate activities against Salmonella enterica and Staphylococcus aureus at all tested concentrations (0.1, 0.2, 0.4, 0.8, 1.6, and 3.2 µM). Furthermore, the in vitro MTT assay exhibited promising anticancer activity against all tested cell lines (hepatocellular carcinoma, mammary gland breast cancer, and colorectal carcinoma colon cancer) with IC50 values ranging from 14.85 to 29.85 µg/mL. These results suggest that the recombinant peptide MzDef may serve as a potential alternative antimicrobial and anticancer agent to be used in medicinal application.

Identification and characterization of two arasin-like peptides in red swamp crayfish Procambarus clarkii

Antimicrobial peptides (AMPs) are small effectors in host defense by directly targeting microorganisms or by indirectly modulating immune responses. In the present study, two arasin like AMPs, named as Pc-arasin1 and Pc-arasin2, were identified in red swamp crayfish Procambarus clarkii with sequence similarity to the arasins found in Hyas araneus. Both Pc-arasins consisted of signal peptide, N-terminal proline-rich region and C-terminal region containing four conserved cysteine residues. The similarity of two Pc-arasins was 44.44%, and Pc-arasin2 contained several additional residues in the N-terminus. Multiple alignment of arasin family suggested the conservation of the C-terminus and the variation of the N-terminus of Pc-arasins. Both AMPs were found hemocytes-specific, and the expression could be induced the challenge of bacteria, espeacially by the pathogenic bacterium Aeromonas hydrophila. Knockdown of each Pc-arasin expression by double strand RNA would suppress the host immunity against A. hydrophila, and the commercially synthetic Pc-arasins could rescue the knockdown consequence. Both synthetic peptide showed broad antimicrobial activity towards 3 Gram-positive bacterium and 3 Gram-negative bacterium, and the minimal inhibitory concentrations varied from 6.25 μM to 50 μM. These results presented new data about the sequence, expression and function of arasin family, and emphasized the role of this family in host immune response against bacterial pathogens. The characterization of Pc-arasins also provided potential of therapeutic agent development for disease control in aquaculture based on these two newly identified AMPs.

Identification, eukaryotic expression and structure & function characterizations of β-defensin like homologues from Pelodiscus sinensis

Defensins are a group of host defense peptides that play a central role in host innate immune responses. Here, 26 genes encoding β-defensin-like peptides have been identified for the first time in Pelodiscus sinensis using database mining approach. Phylogenetic study confirmed that β-defensins are fast evolving genes with high rates of sequence substitutions. The expression level of several selected genes in different tissues was examined by RT-PCR. Ps-BDs mainly adopt β-strands and/or α-helix conformations homology modeled by Rosetta program. Further, Ps-BD2 was expressed in Pichia pastoris and purified using Ni-NTA column and RT-HPLC. As expected, the rPs-BD2 showed strong antimicrobial activity, but displayed a negligible hemolytic and cytotoxic activity on human erythrocytes and Raw 264.7 murine macrophage cells, respectively. Our results suggested that the Ps-BD2 was produced efficiently in P. pastoris expression system, which makes the large-scale use of rPs-BDs possible in the future clinical practice.

Panusin represents a new family of β-defensin-like peptides in invertebrates

Beta_defensin have been solely found in vertebrates until β-defensin-like peptides were described as transcript isoforms in two species of Panulirus genus. They were considered as putative antimicrobials since their biological activity have not been demonstrated. Here we purified and characterized a defensin-like peptide from the hemocytes of spiny lobster P. argus, hereafter named panusin. Structurally, panusin presents a cysteine-stabilized α/β motif, and is prone to form homodimers. Biological activity of panusin showed broad-spectrum antimicrobial activity, characterized for being strikingly salt-resistant. Panusin did not showed hemolytic activity but was demonstrated its binding capacity to different lipid membrane models, indicating amphipathicity of β-sheet core as driving force for its antimicrobial activity. Panusin is considered a new kind of arthropod defensin which share structural and biological features with beta-defensin from vertebrates. The presence of beta-defensin like peptides in crustacean might suggest the emergence of the evolutionary relationship of β-defensins from vertebrates.

Antimicrobial proteins: From old proteins, new tricks

This review describes the main types of antimicrobial peptides (AMPs) synthesised by crustaceans, primarily those identified in shrimp, crayfish, crab and lobster. It includes an overview of their range of microbicidal activities and the current landscape of our understanding of their gene expression patterns in different body tissues. It further summarises how their expression might change following various types of immune challenges. The review further considers proteins or protein fragments from crustaceans that have antimicrobial properties but are more usually associated with other biological functions, or are derived from such proteins. It discusses how these unconventional AMPs might be generated at, or delivered to, sites of infection and how they might contribute to crustacean host defence in vivo. It also highlights recent work that is starting to reveal the extent of multi-functionality displayed by some decapod AMPs, particularly their participation in other aspects of host protection. Examples of such activities include proteinase inhibition, phagocytosis, antiviral activity and haematopoiesis.

Sequence diversity and evolution of antimicrobial peptides in invertebrates

Antimicrobial peptides (AMPs) are evolutionarily ancient molecules that act as the key components in the invertebrate innate immunity against invading pathogens. Several AMPs have been identified and characterized in invertebrates, and found to display considerable diversity in their amino acid sequence, structure and biological activity. AMP genes appear to have rapidly evolved, which might have arisen from the co-evolutionary arms race between host and pathogens, and enabled organisms to survive in different microbial environments. Here, the sequence diversity of invertebrate AMPs (defensins, cecropins, crustins and anti-lipopolysaccharide factors) are presented to provide a better understanding of the evolution pattern of these peptides that play a major role in host defense mechanisms.

The trypsin inhibitor panulirin regulates the prophenoloxidase-activating system in the spiny lobster Panulirus argus

The melanization reaction promoted by the prophenoloxidase-activating system is an essential defense response in invertebrates subjected to regulatory mechanisms that are still not fully understood. We report here the finding and characterization of a novel trypsin inhibitor, named panulirin, isolated from the hemocytes of the spiny lobster Panulirus argus with regulatory functions on the melanization cascade. Panulirin is a cationic peptide (pI 9.5) composed of 48 amino acid residues (5.3 kDa), with six cysteine residues forming disulfide bridges. Its primary sequence was determined by combining Edman degradation/N-terminal sequencing and electrospray ionization-MS/MS spectrometry. The low amino acid sequence similarity with known proteins indicates that it represents a new family of peptidase inhibitors. Panulirin is a competitive and reversible tight-binding inhibitor of trypsin (Ki = 8.6 nm) with a notable specificity because it does not inhibit serine peptidases such as subtilisin, elastase, chymotrypsin, thrombin, and plasmin. The removal of panulirin from the lobster hemocyte lysate leads to an increase in phenoloxidase response to LPS. Likewise, the addition of increasing concentrations of panulirin to a lobster hemocyte lysate, previously depleted of trypsin-inhibitory activity, decreased the phenoloxidase response to LPS in a concentration-dependent fashion. These results indicate that panulirin is implicated in the regulation of the melanization cascade in P. argus by inhibiting peptidase(s) in the pathway toward the activation of the prophenoloxidase enzyme.

Mucosal immunity in the gut: the non-vertebrate perspective

Much is now known about the vertebrate mechanisms involved in mucosal immunity, and the requirement of commensal microbiota at mucosal surfaces for the proper functioning of the immune system. In comparison, very little is known about the mechanisms of immunity at the barrier epithelia of non-vertebrate organisms. The purpose of this review is to summarize key experimental evidence illustrating how non-vertebrate immune mechanisms at barrier epithelia compare to those of higher vertebrates, using the gut as a model organ. Not only effector mechanisms of gut immunity are similar between vertebrates and non-vertebrates, but it also seems that the proper functioning of non-vertebrate gut defense mechanisms requires the presence of a resident microbiota. As more information becomes available, it will be possible to obtain a more accurate picture of how mucosal immunity has evolved, and how it adapts to the organisms' life styles.