A novel antimicrobial peptide from Bufo bufo gargarizans

Bacterial clustering biomaterials as anti-infective therapies

In Nature, bacterial clustering by host-released peptides or nucleic acids is an evolutionarily conserved immune defense strategy employed to prevent adhesion of pathogenic microbes, which is prerequisite for most infections. Synthetic anti-adhesion strategies present as non-lethal means of targeting bacteria and may potentially be used to avoid resistance against antimicrobial therapies. From bacteria-agglutinating biomolecules discovered in nature to synthetic designs involving peptides, cationic polymers and nanoparticles, the modes of actions appear broad and unconsolidated. Herein, we present a critical review and update of the state-of-the-art in synthetic bacteria-clustering designs with proposition of a more streamlined nomenclature and classification. Overall, this review aims to consolidate the conceptual framework in the field of bacterial clustering and highlight its potentials as an avenue for discovering novel antibacterial biomaterials.

Fabrication and Characterization of Buforin I-Loaded Electrospun Chitosan/Polyethylene Oxide Nanofibrous Membranes with Antimicrobial Activity for Food Packing Applications

The rising resistance of bacteria to antibiotics has driven the search for new antimicrobial agents. This study focused on encapsulating Buforin I, an antimicrobial peptide, in chitosan/polyethylene oxide (CS-PEO) nanofibers. Buforin I was loaded at a minimum bactericidal concentration (MBC), 10× MBC, and 20× MBC, with assessments on morphology, thermal properties, chemical bonds, crystalline structure, mechanical strength, antimicrobial activity, and cell toxicity. Techniques like differential scanning calorimetry and Fourier-transform infrared spectroscopy confirmed the effective loading of Buforin I in the nanofibers. Scanning electron microscopy showed that Buforin incorporation increased nanofiber diameters. The tensile strength peaked at 20× MBC. Microbial tests indicated that the inhibition zone for nanofibers at 20× MBC surpassed that of commercial antibiotics. Beef coated with CS-PEO nanofibers containing Buforin I demonstrated reduced pH and water activity, alongside lower weight loss during storage. Texture and color analyses revealed that the Buforin I nanofibers helped maintain beef hardness and slowed color degradation compared to control samples. Moreover, thiobarbituric acid levels and total microbial counts in the coated beef were significantly lower than controls (below 3 log CFU/g after 9 days at 4 °C). Thus, these nanofibers may serve as effective antimicrobial packaging agents to delay food spoilage.

Current developments and prospects of the antibiotic delivery systems

Antibiotics have remained the cornerstone for the treatment of bacterial infections ever since their discovery in the twentieth century. The uproar over antibiotic resistance among bacteria arising from genome plasticity and biofilm development has rendered current antibiotic therapies ineffective, urging the development of innovative therapeutic approaches. The development of antibiotic resistance among bacteria has further heightened the clinical failure of antibiotic therapy, which is often linked to its low bioavailability, side effects, and poor penetration and accumulation at the site of infection. In this review, we highlight the potential use of siderophores, antibodies, cell-penetrating peptides, antimicrobial peptides, bacteriophages, and nanoparticles to smuggle antibiotics across impermeable biological membranes to achieve therapeutically relevant concentrations of antibiotics and combat antimicrobial resistance (AMR). We will discuss the general mechanisms via which each delivery system functions and how it can be tailored to deliver antibiotics against the paradigm of mechanisms underlying antibiotic resistance.

Evaluating the impact of cell-penetrating motif position on the cellular uptake of magnetite nanoparticles

Cell-penetrating peptides (CPPs) have been employed to enhance the cellular uptake and intracellular delivery of various nanocarriers. Among them, nanoparticles (NPs) have been used as suitable vehicles for delivering different bioactive molecules in the treatment of a diverse range of diseases. Given the pivotal role of the conjugation method of CPPs, this study aims to evaluate the impact of the position of a cell-penetrating motif (LFVCR) on the biocompatibility, cellular uptake, and endosomal escape of magnetite NPs. The designed peptide's physicochemical properties suggest they are well-suited for efficient cell penetration with minimal cytotoxicity. The resulting designed nanoconjugates were characterized using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), dynamic light scattering (DLS), and transmission electron microscopy (TEM). The results indicate that motif position significantly impacts the cellular uptake and endosomal escape of the designed nanobioconjugates. Key findings suggest that motif exposure enhances endocytosis-mediated cell internalization and improves endosomal escape efficiency. These results were compared with nanobioconjugates displaying previously reported CPPs. The selected nanobioconjugate demonstrated superior performance in endosomal escape and comparable cell uptake to the reference nanobioconjugates. These results, along with the nanobioconjugate's physicochemical characteristics and high biocompatibility, position the nanocarrier as a suitable candidate for delivering diverse bioactive molecules.

Histone H1 kills MRSA

The antimicrobial activity of histones was discovered in the 1940s, but their mechanism of action is not fully known. Here we show that methicillin-resistant Staphylococcus aureus (MRSA) is susceptible to histone H1 (H1), even in the presence of divalent cations and serum. Through selective evolution and a genome-wide screen of a transposon library, as well as physiological and pharmacological experiments, we elucidated how H1 kills MRSA. We show that H1 first binds to wall teichoic acids with high affinity. Once bound, H1 requires a potentiated membrane and a metabolically active bacterium to permeabilize the membrane and enter the cell. Upon entry, H1 accumulates intracellularly, in close association with the bacterial DNA. Of note, anti-H1 antibodies inhibit neutrophil extracellular trap killing of MRSA. Moreover, H1 colocalizes with bacterial DNA in abscess samples of MRSA-infected patients, suggesting a role for H1 in combating MRSA in vivo.

Advancements in peptide-based antimicrobials: A possible option for emerging drug-resistant infections

In recent years, multidrug-resistant pathogenic microorganisms (MDROs) have emerged as a severe threat to human health, exhibiting robust resistance to traditional antibiotics. This has created a formidable challenge in modern medicine as we grapple with limited options to combat these resilient bacteria. Despite extensive efforts by scientists to develop new antibiotics targeting these pathogens, the quest for novel antibacterial molecules has become increasingly arduous. Fortunately, nature offers a potential solution in the form of cationic antimicrobial peptides (AMPs) and their synthetic counterparts. AMPs, naturally occurring peptides, have displayed promising efficacy in fighting bacterial infections by disrupting bacterial cell membranes, hindering their survival and reproduction. These peptides, along with their synthetic mimics, present an exciting alternative in combating antibiotic resistance. They hold the potential to emerge as a formidable tool against MDROs, offering hope for improved strategies to protect communities. Extensive research has explored the diversity, history, and structure-properties relationship of AMPs, investigating their amphiphilic nature for membrane disruption and mechanisms of action. However, despite their therapeutic promise, AMPs face several documented limitations. Among these challenges, poor pharmacokinetic properties stand out, impeding the attainment of therapeutic levels in the body. Additionally, some AMPs exhibit toxicity and susceptibility to protease cleavage, leading to a short half-life and reduced efficacy in animal models. These limitations pose obstacles in developing effective treatments based on AMPs. Furthermore, the high manufacturing costs associated with AMPs could significantly hinder their widespread use. In this review, we aim to present experimental and theoretical insights into different AMPs, focusing specifically on antibacterial peptides (ABPs). Our goal is to offer a concise overview of peptide-based drug candidates, drawing from a wide array of literature and peer-reviewed studies. We also explore recent advancements in AMP development and discuss the challenges researchers face in moving these molecules towards clinical trials. Our main objective is to offer a comprehensive overview of current AMP and ABP research to guide the development of more precise and effective therapies for bacterial infections.

Unveiling Encrypted Antimicrobial Peptides from Cephalopods' Salivary Glands: A Proteolysis-Driven Virtual Approach

Antimicrobial peptides (AMPs) have potential against antimicrobial resistance and serve as templates for novel therapeutic agents. While most AMP databases focus on terrestrial eukaryotes, marine cephalopods represent a promising yet underexplored source. This study reveals the putative reservoir of AMPs encrypted within the proteomes of cephalopod salivary glands via in silico proteolysis. A composite protein database comprising 5,412,039 canonical and noncanonical proteins from salivary apparatus of 14 cephalopod species was subjected to digestion by 5 proteases under three protocols, yielding over 9 million of nonredundant peptides. These peptides were effectively screened by a selection of 8 prediction and sequence comparative tools, including machine learning, deep learning, multiquery similarity-based models, and complex networks. The screening prioritized the antimicrobial activity while ensuring the absence of hemolytic and toxic properties, and structural uniqueness compared to known AMPs. Five relevant AMP datasets were released, ranging from a comprehensive collection of 542,485 AMPs to a refined dataset of 68,694 nonhemolytic and nontoxic AMPs. Further comparative analyses and application of network science principles helped identify 5466 unique and 808 representative nonhemolytic and nontoxic AMPs. These datasets, along with the selected mining tools, provide valuable resources for peptide drug developers.

Unveiling mechanisms of antimicrobial peptide: Actions beyond the membranes disruption

Antimicrobial peptides (AMPs) are a critical component of the innate immune system, playing a key role in defending against a variety of pathogenic microorganisms. While many AMPs act primarily on the cell membrane of target pathogens, leading to lysis and subsequent cell death, less is known about their nonlytic membrane activity. This nonlytic activity allows AMPs to target and disrupt bacterial cells without causing lysis, leading to bacterial death through alternative mechanisms.Understanding these nonlytic properties of AMPs is crucial, as they present a promising alternative to traditional antibiotics, which can induce bacterial resistance and have adverse effects on human health and the environment. The mechanisms by which AMPs exhibit nonlytic membrane activity are still being explored. However, it is believed that AMPs penetrate the bacterial membrane and interact directly with internal cellular components such as DNA, RNA, and various enzymes essential for microbial survival and replication. This interaction disrupts metabolic homeostasis, ultimately resulting in bacterial death.The nonlytic activity of AMPs also results in minimal damage to host cells and tissues, making them attractive candidates for the development of new, more effective antibiotics. This review emphasizes the mechanisms by which AMPs nonlytically target cellular components, including DNA, proteins, RNA, and other biomolecules, and discusses their clinical significance. Understanding these mechanisms may pave the way for developing alternatives to conventional antibiotics, offering a solution to the growing issue of antibiotic resistance.

From inside to outside: exploring extracellular antimicrobial histone-derived peptides as multi-talented molecules

The emergence of bacterial resistance to antibiotics poses a global health threat, necessitating innovative solutions. The contemporary challenge lies in bacterial resistance, impacting morbidity, mortality, and global economies. Antimicrobial peptides (AMPs) offer a promising avenue for addressing antibiotic resistance. The Antimicrobial Peptide Database catalogs 3569 peptides from various organisms, representing a rich resource for drug development. Histones, traditionally recognized for their role in nucleosome structures, have gained attention for their extracellular functions, including antimicrobial and immunomodulatory properties. This review aims to thoroughly investigate antimicrobial peptides derived from histones in various organisms, elucidating their mechanisms. In addition, it gives us clues about how extracellular histones might be used in drug delivery systems to fight bacterial infections. This comprehensive analysis emphasizes the importance of histone-derived peptides in developing innovative therapeutic strategies for evolving bacterial challenges.

Insect meal in aquafeeds: A sustainable path to enhanced mucosal immunity in fish

The mucosal surfaces of fish, including their intestines, gills, and skin, are constantly exposed to various environmental threats, such as water quality fluctuations, pollutants, and pathogens. However, various cells and microbiota closely associated with these surfaces work in tandem to create a functional protective barrier against these conditions. Recent research has shown that incorporating specific feed ingredients into fish diets can significantly boost their mucosal and general immune response. Among the various ingredients being investigated, insect meal has emerged as one of the most promising options, owing to its high protein content and immunomodulatory properties. By positively influencing the structure and function of mucosal surfaces, insect meal (IM) has the potential to enhance the overall immune status of fish. This review provides a comprehensive overview of the potential benefits of incorporating IM into aquafeed as a feed ingredient for augmenting the mucosal immune response of fish.

Histone derived antimicrobial peptides identified from Mytilus coruscus serum by peptidomics

Histones and their N-terminal or C-terminal derived peptides have been studied in vertebrates and presented as potential antimicrobial agents playing important roles in the innate immune defenses. Although histones and their derived peptides had been reported as components of innate immunity in invertebrates, the knowledge about the histone derived antimicrobial peptides (HDAPs) in invertebrates are still limited. Using a peptidomic technique, a set of peptide fragments derived from the histones was identified in this study from the serum of microbes challenged Mytilus coruscus. Among the 85 identified histone-derived-peptides with high confidence, 5 HDAPs were chemically synthesized and the antimicrobial activities were verified, showing strong growth inhibition against Gram-positive bacteria, Gram-negative bacteria, and fungus. The gene expression level of the precursor histones matched by representative HDAPs were further tested using q-PCR, and the results showed a significant upregulation of the histone gene expression levels in hemocytes, gill, and mantle of the mussel after immune stress. In addition, three identified HDAPs were selected for preparation of specific antibodies, and the corresponding histones and their derived C-terminal fragments were detected by Western blotting in the blood cell and serum of immune challenged mussel, respectively, indicating the existence of HDAPs in M. coruscus. Our findings revealed the immune function of histones in Mytilus, and confirmed the existence of HDAPs in the mussel. The identified Mytilus HDAPs represent a new source of immune effector with antimicrobial function in the innate immune system, and thus provide promising candidates for the treatment of microbial infections in aquaculture and medicine.

Novel non-helical antimicrobial peptides insert into and fuse lipid model membranes

This research addresses the growing menace of antibiotic resistance by exploring antimicrobial peptides (AMPs) as alternatives to conventional antibiotics. Specifically, we investigate two linear amphipathic AMPs, LE-53 (12-mer) and LE-55 (16-mer), finding that the shorter LE-53 exhibits greater bactericidal activity against both Gram-negative (G(-)) and Gram-positive (G(+)) bacteria. Remarkably, both AMPs are non-toxic to eukaryotic cells. The heightened effectiveness of LE-53 is attributed to its increased hydrophobicity (H) compared to LE-55. Circular dichroism (CD) reveals that LE-53 and LE-55 both adopt β-sheet and random coil structures in lipid model membranes (LMMs) mimicking G(-) and G(+) bacteria, so secondary structure is not the cause of the potency difference. X-ray diffuse scattering (XDS) reveals increased lipid chain order in LE-53, a potential key distinction. Additionally, XDS study uncovers a significant link between LE-53's upper hydrocarbon location in G(-) and G(+) LMMs and its efficacy. Neutron reflectometry (NR) confirms the AMP locations determined using XDS. Solution small angle X-ray scattering (SAXS) demonstrates LE-53's ability to induce vesicle fusion in bacterial LMMs without affecting eukaryotic LMMs, offering a promising strategy to combat antibiotic-resistant strains while preserving human cell integrity, whereas LE-55 has a smaller ability to induce fusion.

A Comprehensive Review of Patented Antimicrobial Peptides from Amphibian Anurans

Since the 1980s, studies of antimicrobial peptides (AMPs) derived from anuran skin secretions have unveiled remarkable structural diversity and a wide range of activities. This study explores the potential of these peptides for drug development by examining granted patents, amino acid modifications related to patented peptides, and recent amphibians' taxonomic updates influencing AMP names. A total of 188 granted patents related to different anuran peptides were found, with Asia and North America being the predominant regions, contributing 65.4% and 15.4%, respectively. Conversely, although the Neotropical region is the world's most diversified region for amphibians, it holds only 3.7% of the identified patents. The antimicrobial activities of the peptides are claimed in 118 of these 188 patents. Additionally, for 160 of these peptides, 66 patents were registered for the natural sequence, 69 for both natural and derivative sequences, and 20 exclusively for sequence derivatives. Notably, common modifications include alterations in the side chains of amino acids and modifications to the peptides' N- and C-termini. This review underscores the biomedical potential of anuran-derived AMPs, emphasizing the need to bridge the gap between AMP description and practical drug development while highlighting the urgency of biodiversity conservation to facilitate biomedical discoveries.

Centrosomal protein of 192 kDa (Cep192) fragment possesses bactericidal and parasiticidal activities in Larimichthys crocea

A novel AMP Lc1773, derived from centrosomal protein of 192 kDa (Cep192), was isolated from Larimichthys crocea using a Bacillus subtilis system. After cDNA libraries construction, repeating selection of B. subtilis system, extraction of extracellular protein, and expression of recombinant protein, we found that B. subtilis 1773, extracellular protein, and rLc1773 had a strong potential to kill Vibrio. parahaemolyticus and V. vulnificus. Further analysis of the antibacterial mechanism revealed that rLc1773 not only disrupted the integrity of bacterial membrane (as confirmed by SEM, TEM, and confocal microscopy observation, and flow cytometry assays), resulting in bacterial cell membrane pore conformation, bacterial rupture, and leakage of cellular contents, but also targeted to block protein synthesis rather than damage nucleic acids (as confirmed by SDS-PAGE, enzyme expression, and gel retardation assays). In addition, rLc1773 had the ability to kill parasite Scuticociliatida in a high rate and low concentration. Critically, the antibacterial activity of rLc1773 had good thermal stability and UV radiation tolerance, but it was affected by pH 9-11 and diverse enzyme to some extent. Lc1773 had neither hemolysis on fish, shrimp, and rabbit erythrocytes，nor significant cytotoxicity. To our knowledge, Cep192 fragment was first demonstrated to possess bactericidal and parasiticidal activities.

WITHDRAWN: Photobuforin II, a fluorescent photoswitchable peptide

The Publisher regrets that this article is an accidental duplication of an article that has already been published, https://doi.org/10.1016/j.bbadva.2023.100106. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/policies/article-withdrawal.

Photobuforin II, a fluorescent photoswitchable peptide

Antimicrobial peptide buforin II translocates across the cell membrane and binds to DNA. Its sequence is identical to a portion of core histone protein H2A making it a highly charged peptide. Buforin II has a proline residue in the middle of its sequence that creates a helix-hinge-helix motif which has been found to play a key role in its ability to translocate across the cell membrane. To explore the structure-function relationship of this proline residue this study has replaced P11 with a meta-substituted azobenzene amino acid (Z). The resultant peptide, photobuforin II, retained the secondary structure and membrane activity of the naturally occurring peptide while gaining new spectroscopic properties. Photobuforin II can be isomerized from its trans to cis isomer upon irradiation with ultra-violet (UV) light and from its cis to trans isomer upon irradiation with visible (VL). Photobuforin II is also fluorescent with an emission peak at 390 nm. The intrinsic fluorescence of the peptide was used to determine binding to the membrane and to DNA. VL-treated photobuforin II has a 2-fold lower binding constant compared to UV-treated photobuforin and causes 11-fold more membrane leakage in 3:1 POPC:POPG vesicles. Photobuforin II provides insights into the importance of structure function relationships in membrane active peptides while also demonstrating that azobenzene can be used in certain peptide sequences to produce intrinsic fluorescence.

An Update on the Therapeutic Potential of Antimicrobial Peptides against Acinetobacter baumannii Infections

The rise in antibiotic-resistant strains of clinically important pathogens is a major threat to global health. The World Health Organization (WHO) has recognized the urgent need to develop alternative treatments to address the growing list of priority pathogens. Antimicrobial peptides (AMPs) rank among the suggested options with proven activity and high potential to be developed into effective drugs. Many AMPs are naturally produced by living organisms protecting the host against pathogens as a part of their innate immunity. Mechanisms associated with AMP actions include cell membrane disruption, cell wall weakening, protein synthesis inhibition, and interference in nucleic acid dynamics, inducing apoptosis and necrosis. Acinetobacter baumannii is a critical pathogen, as severe clinical implications have developed from isolates resistant to current antibiotic treatments and conventional control procedures, such as UV light, disinfectants, and drying. Here, we review the natural AMPs representing primary candidates for new anti-A. baumannii drugs in post-antibiotic-era and present computational tools to develop the next generation of AMPs with greater microbicidal activity and reduced toxicity.

Application of Cell Penetrating Peptides as a Promising Drug Carrier to Combat Viral Infections

Novel effective drugs or therapeutic vaccines have been already developed to eradicate viral infections. Some non-viral carriers have been used for effective drug delivery to a target cell or tissue. Among them, cell penetrating peptides (CPPs) attracted a special interest to enhance drug delivery into the cells with low toxicity. They were also applied to transfer peptide/protein-based and nucleic acids-based therapeutic vaccines against viral infections. CPPs-conjugated drugs or vaccines were investigated in several viral infections including poliovirus, Ebola, coronavirus, herpes simplex virus, human immunodeficiency virus, hepatitis B virus, hepatitis C virus, Japanese encephalitis virus, and influenza A virus. Some studies showed that the uptake of CPPs or CPPs-conjugated drugs can be performed through both non-endocytic and endocytic pathways. Despite high potential of CPPs for cargo delivery, there are some serious drawbacks such as non-tissue-specificity, instability, and suboptimal pharmacokinetics features that limit their clinical applications. At present, some solutions are utilized to improve the CPPs properties such as conjugation of CPPs with targeting moieties, the use of fusogenic lipids, generation of the proton sponge effect, etc. Up to now, no CPP or composition containing CPPs has been approved by the Food and Drug Administration (FDA) due to the lack of sufficient in vivo studies on stability, immunological assays, toxicity, and endosomal escape of CPPs. In this review, we briefly describe the properties, uptake mechanisms, advantages and disadvantages, and improvement of intracellular delivery, and bioavailability of cell penetrating peptides. Moreover, we focus on their application as an effective drug carrier to combat viral infections.

Identification, Screening and Antibacterial Mechanism Analysis of Novel Antimicrobial Peptides from Sturgeon (Acipenser ruthenus) Spermary

Fish is an important source of antimicrobial peptides. This study aimed to identify and screen antibacterial peptides with excellent antibacterial activity derived from sturgeon spermary peptides (SSPs) and to analyze their antibacterial activity and mechanism. Liquid chromatography-mass spectrometry/mass spectrometry methods were used to analyze and identify peptide sequences, computational prediction tool and molecular docking methods were used for virtual screening of antimicrobial peptides, and finally, candidate peptides were synthesized by solid-phase synthesis method. The results demonstrate that SSPs have excellent inhibitory activity against Escherichia coli with an inhibitory rate of 76.46%. Most parts of the SSPs were derived from the sturgeon (Acipenser ruthenus) histones, and the coverage of histone H2B was the highest (45%). Two novel peptides (NDEELNKLM and RSSKRRQ) were obtained by in silico prediction tools and molecular docking, which may interact with the DNA gyrase and dihydrofolate reductase of E. coli by forming salt bridges and hydrogen bonds. Compared to the individual peptides, the antibacterial effect was significantly improved by mixing the two peptides in equal proportions. Two novel peptides change the permeability of the E. coli cell membranes and may exert antimicrobial activity by inhibiting the metabolic process of the nucleic acids.

Preliminary investigation of the immune activity of PmH2A-derived antimicrobial peptides from the pearl oyster Pinctada fucata martensii

Antimicrobial peptides (AMPs) play important roles in the immune defense against pathogenic microorganisms. For instance, histone 2A (H2A)-derived AMPs is an antimicrobial peptide involved in the host's innate immune defense and immunoregulation. AMPs have been isolated from the pearl oyster Pinctada fucata martensii but their role in host defense remains poorly understood. To elucidate the structural features of P. f. martensii H2A (PmH2A)-derived AMPs and their potential immune functions, we synthesized a series of laboratory-designed synthetic analogs of PmH2A and examined their antimicrobial properties, as well as their mechanisms of action. This analysis revealed inhibitory effects on the growth of Gram-positive and Gram-negative bacteria. Further assessment by transmission electron microscopy (TEM) of two of the three peptides, PmH2A-AMP and PmH2A-AMP(5-13)[KLLK]₃, confirmed that it exerted an anti-bacterial activity through membrane lysis. Finally, we found that the hemocytes and gills of P. f. martensii released antimicrobial H2A histones in response to LPS exposure, mimicking tissue damage and infection. This immune response is reminiscent of the neutrophil extracellular traps (NETs) recently described in oysters. Thus, the LPS challenge is sufficient to induce histone-derived peptide accumulation in pearl oyster P.f. martensii.

Antimicrobial Compounds from Skin Secretions of Species That Belong to the Bufonidae Family

Skin secretions of toads are a complex mixture of molecules. The substances secreted comprise more than 80 different compounds that show diverse pharmacological activities. The compounds secreted through skin pores and parotid glands are of particular interest because they help toads to endure in habitats full of pathogenic microbes, i.e., bacteria, fungi, viruses, and protozoa, due to their content of components such as bufadienolides, alkaloids, and antimicrobial peptides. We carried out an extensive literature review of relevant articles published until November 2022 in ACS Publications, Google Scholar, PubMed, and ScienceDirect. It was centered on research addressing the biological characterization of the compounds identified in the species of genera Atelopus, Bufo, Duttaphrynus, Melanophryniscus, Peltopryne, Phrynoidis, Rhaebo, and Rhinella, with antibacterial, antifungal, antiviral, and antiparasitic activities; as well as studies performed with analogous compounds and skin secretions of toads that also showed these activities. This review shows that the compounds in the secretions of toads could be candidates for new drugs to treat infectious diseases or be used to develop new molecules with better properties from existing ones. Some compounds in this review showed activity against microorganisms of medical interest such as Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Coronavirus varieties, HIV, Trypanosoma cruzi, Leishmania chagasi, Plasmodium falciparum, and against different kinds of fungi that affect plants of economic interest.

Prospects of antimicrobial peptides as an alternative to chemical preservatives for food safety

Antimicrobial peptides (AMPs) are a potential alternative to antimicrobial agents that have got considerable research interest owing to their significant role in the inhibition of bacterial pathogens. These AMPs can essentially inhibit the growth and multiplication of microbes through multiple mechanisms including disruption of cellular membranes, inhibition of cell wall biosynthesis, or affecting intracellular components and cell division. Moreover, AMPs are biocompatible and biodegradable therefore, they can be a good alternative to antimicrobial agents and chemical preservatives. A few of their features for example thermostability and high selectivity are quite appealing for their potential use in the food industry for food preservation to prevent the spoilage caused by microorganisms and foodborne pathogens. Despite these advantages, very few AMPs are being used at an industrial scale for food preservation as these peptides are quite vulnerable to external environmental factors which deter their practical applications and commercialization. The review aims to provide an outline of the mechanism of action of AMPs and their prospects as an alternative to chemical preservatives in the food industry. Further studies related to the structure-activity relationship of AMPs will help to expand the understanding of their mechanism of action and to determine specific conditions to increase their stability and applicability in food preservation.

Functional characterization of a histone H2A derived antimicrobial peptide HARRIOTTIN-1 from sicklefin chimaera, Neoharriotta pinnata

Antimicrobial peptides (AMPs) are gene encoded short peptides which play an important role in the innate immunity of almost all living organisms ranging from bacteria to mammals. Histones play a very important role in defense as precursors to bioactive peptides. The present study is an attempt to decipher the antimicrobial activity of a histone H2A derived peptide, Harriottin-1 from sicklefin chimaera, Neoharriotta pinnata. Analysis in silico predicted the molecule with potent antibacterial and anticancer property. The Harriottin-1 was recombinantly produced and the recombinant peptide rHar-1 demonstrated potent antibacterial activity at 25 μM besides anticancer activity. The study strongly suggests the importance of histone H2A derived peptides as a model for the design and synthesis of potent peptide drugs.

An Overview of the Potentialities of Antimicrobial Peptides Derived from Natural Sources

Antimicrobial peptides (AMPs) are constituents of the innate immune system in every kind of living organism. They can act by disrupting the microbial membrane or without affecting membrane stability. Interest in these small peptides stems from the fear of antibiotics and the emergence of microorganisms resistant to antibiotics. Through membrane or metabolic disruption, they defend an organism against invading bacteria, viruses, protozoa, and fungi. High efficacy and specificity, low drug interaction and toxicity, thermostability, solubility in water, and biological diversity suggest their applications in food, medicine, agriculture, animal husbandry, and aquaculture. Nanocarriers can be used to protect, deliver, and improve their bioavailability effectiveness. High cost of production could limit their use. This review summarizes the natural sources, structures, modes of action, and applications of microbial peptides in the food and pharmaceutical industries. Any restrictions on AMPs' large-scale production are also taken into consideration.

Combining mass spectrometry and machine learning to discover bioactive peptides

Peptides play important roles in regulating biological processes and form the basis of a multiplicity of therapeutic drugs. To date, only about 300 peptides in human have confirmed bioactivity, although tens of thousands have been reported in the literature. The majority of these are inactive degradation products of endogenous proteins and peptides, presenting a needle-in-a-haystack problem of identifying the most promising candidate peptides from large-scale peptidomics experiments to test for bioactivity. To address this challenge, we conducted a comprehensive analysis of the mammalian peptidome across seven tissues in four different mouse strains and used the data to train a machine learning model that predicts hundreds of peptide candidates based on patterns in the mass spectrometry data. We provide in silico validation examples and experimental confirmation of bioactivity for two peptides, demonstrating the utility of this resource for discovering lead peptides for further characterization and therapeutic development.

Dual Roles of Extracellular Histone H3 in Host Defense: Its Differential Regions Responsible for Antimicrobial and Cytotoxic Properties and Their Modes of Action

Extracellular histones play a dual role—antimicrobial and cytotoxic—in host defense. In this study, we evaluated the antimicrobial and cytotoxic activities of histone H3 and identified the responsible molecular regions for these properties. Broth microdilution assays indicated that histone H3 exhibits growth inhibitory activity against not only Gram-negative and -positive bacteria but also fungi. Observations under scanning electron microscopy (SEM) revealed that histone H3 induced morphological abnormalities on the cell surface of a wide range of reference pathogens. MTT assays and SEM observations indicated that histone H3 has strong cytotoxic and cell lytic effects on mammalian normal, immortal, and tumor cell lines. Assays using synthetic peptides corresponding to fragments 1–34 (H3DP1), 35–68 (H3DP2), 69–102 (H3DP3), and 103–135 (H3DP4) of histone H3 molecule demonstrated that its antimicrobial activity and cytotoxicity are elicited by the H3DP2 and H3DP3 protein regions, respectively. Enzyme-linked endotoxin binding assays indicated that histones H3 and H3DP1, H3DP2, and H3DP4, but not H3DP3, exhibited high affinities toward lipopolysaccharide and lipoteichoic acid. Our findings are expected to contribute to the development of new histone H3-based peptide antibiotics that are not cytotoxic.

Interaction of RecA mediated SOS response with bacterial persistence, biofilm formation, and host response

Antibiotics have a primary mode of actions, and most of them have a common secondary mode of action via reactive species (ROS and RNS) mediated DNA damage. Bacteria have been able to tolerate this DNA damage by SOS (Save-Our-Soul) response. RecA is the universal essential key protein of the DNA damage mediated SOS repair in various bacteria including ESKAPE pathogens. In addition, antibiotics also triggers activation of various other bacterial mechanisms such as biofilm formation, host dependent responses, persister subpopulation formation. These supporting the survival of bacteria in unfriendly natural conditions i.e. antibiotic presence. This review highlights the detailed mechanism of RecA mediated SOS response as well as role of RecA-LexA interaction in SOS response. The review also focuses on inter-connection between DNA damage repair pathway (like SOS response) with other survival mechanisms of bacteria such as host mediated RecA induction, persister-SOS interplay, and biofilm-SOS interplay. This understanding of inter-connection of SOS response with different other survival mechanisms will prove beneficial in targeting the SOS response for prevention and development of therapeutics against recalcitrant bacterial infections. The review also covers the significance of RecA as a promising potent therapeutic target for hindering bacterial SOS response in prevailing successful treatments of bacterial infections and enhancing the conventional antibiotic efficiency.

Evaluation of the antileishmanial effect of polyclonal antibodies and cationic antimicrobial peptides

Leishmaniasis is one of the tropical and subtropical diseases which, according to WHO, has the priority of control. The list of anti-leishmanial drugs is limited and requires side effects, high costs, and long-term treatments. Various species, parasite resistance, and simultaneous diseases are among the factors that affect the effectiveness of treatment. Due to these problems and based on satisfactory records of previous studies using antimicrobial peptides (AMPs) against infectious diseases, this study aimed to evaluate the antileishmanial effect of Leishmania-infected macrophage polyclonal antibody (LIMPA) with or without different concentrations (2, 4, 6, 8, 10, 20, 40, 60, and 100 µg/ml) of CM11 and (40, 80, and 100 µg/ml) BufIIIb, two AMPs, in vitro and their therapeutic effects against CL of Balb/c mice. Results showed that LIMPA induced an anti-proliferative effect on Leishmania major growth in macrophages in vitro and intramacrophage-amastigotes in vivo. CM11 with IC50 of 8.73 and 10.10 μg/ml at 48 hours, and BufIIIb with IC50 of 66.83 and 80.26 μg/ml, at 24 hours showed the most significant inhibition of L. major promastigotes and amastigotes. In addition, the CM11 and BufIIIb, with a CC50 of 9.7 μg/ml and 40.34 μg/ml, showed the most significant inhibition effect on the J774.A1 cell line at 48 hours, respectively. In addition, in vivo experiments using LIMPA with a 0.01 mg/kg dosage showed a significant difference (p < 0.001) in the last week of the measurement compared to the control. The results of this study may be a promising prospect for further investigations.

A novel hybrid peptide composed of LfcinB6 and KR-12-a4 with enhanced antimicrobial, anti-inflammatory and anti-biofilm activities

Hybridizing two known antimicrobial peptides (AMPs) is a simple and effective strategy for designing antimicrobial agents with enhanced cell selectivity against bacterial cells. Here, we generated a hybrid peptide Lf-KR in which LfcinB6 and KR-12-a4 were linked with a Pro hinge to obtain a novel AMP with potent antimicrobial, anti-inflammatory, and anti-biofilm activities. Lf-KR exerted superior cell selectivity for bacterial cells over sheep red blood cells. Lf-KR showed broad-spectrum antimicrobial activities (MIC: 4–8 μM) against tested 12 bacterial strains and retained its antimicrobial activity in the presence of salts at physiological concentrations. Membrane depolarization and dye leakage assays showed that the enhanced antimicrobial activity of Lf-KR was due to increased permeabilization and depolarization of microbial membranes. Lf-KR significantly inhibited the expression and production of pro-inflammatory cytokines (nitric oxide and tumor necrosis factor‐α) in LPS-stimulated mouse macrophage RAW264.7 cells. In addition, Lf-KR showed a powerful eradication effect on preformed multidrug-resistant Pseudomonas aeruginosa (MDRPA) biofilms. We confirmed using confocal laser scanning microscopy that a large portion of the preformed MDRPA biofilm structure was perturbed by the addition of Lf-KR. Collectively, our results suggest that Lf-KR can be an antimicrobial, anti-inflammatory, and anti-biofilm candidate as a pharmaceutical agent.

Conformational Transition-Triggered Disassembly of Therapeutic Peptide Nanomedicine for Tumor Therapy

Cationic therapeutic peptides have received widespread attention due to their excellent antibacterial and antitumor properties. However, most of these peptides have undesirable delivery efficiency and high hemolytic toxicity due to the positively charged α-helix structure containing many lysine and arginine, which may restrict its in vivo applications. Herein, a conformationally transformed therapeutic peptide Pep-HCO₃ modified with bicarbonates on guanidine groups is designed. Such a design allows Pep-HCO₃ ((nap-RAGLQFPVGRLLRRLLRRLLR) nHCO₃ ) to self-assemble into nanoparticles (NP-Pep) due to disrupting helix folding and the formation of intermolecular hydrogen bonding between bicarbonates and guanidine groups. When pH is from 7.4 to 6.5 at the tumor sites, guanidine bicarbonate can be hydrolyzed to form CO₂ and guanidine groups, resulting in the disassembling of the NP-Pep into monomers α-Pep with a positively charged α-helix structure. In vivo, NP-Pep not only inhibits the tumor growth of xenografted mice with a twofold enhanced inhibition rate compared with α-Pep treatment group, but also significantly reduces the hemolytic toxicity by responding to the pH of tumor microenvironment. Therefore, the strategy of conformational transition-triggered disassembly of nanoparticles allows efficient delivery of cationic therapeutic peptides and lowering the hemolytic toxicity, which may provide an avenue for developing high-performance cationic peptide in vivo applications.

Buforin I an alternative to conventional antibiotics: Evaluation of the antimicrobial properties, stability, and safety

Cationic antimicrobial peptides are being developed as a promising class of antimicrobial sub-stances. The introduction of a new antibiotic component requires a comprehensive study of its properties so that it can be relied upon to continue laboratory procedures and clinical trials on laboratory animals or human volunteers. Antimicrobial activity of buforin I was evaluated against 15 of the most important pathogenic bacterial and fungal strains. This was followed by assessing anti-biofilm activity, time-dependent inhibitory, thermal stability, plas-ma stability, hemolysis, and cytotoxic activities. The range of obtained MICs was between 4 and 16 μg/mL. The most resistant and most sensitive microbial strains were S. salivarius and C. perfringens, respectively. Buforin I not only inhibited biofilm formation, but also showed a high biofilm radiation activity. Buforin I was stable in human plasma and also at different temperatures including 40, 60, and 80 °C. Although no significant anti-cancer properties were observed for buforin I, the lack of cytotoxicity as well as the lack of hemolytic activity confirm its safety. The high therapeutic index indicated that buforin I has a considerable pharmaceutical potential and can be a reasonable candidate to replace antibiotics or administered in combination with antibiotics to increase the effectiveness as well as reduce the dose of antibiotics.

Translocation of non-lytic antimicrobial peptides and bacteria penetrating peptides across the inner membrane of the bacterial envelope

The increase in multidrug-resistant pathogenic bacteria has become a problem worldwide. Currently there is a strong focus on the development of novel antimicrobials, including antimicrobial peptides (AMP) and antimicrobial antisense agents. While the majority of AMP have membrane activity and kill bacteria through membrane disruption, non-lytic AMP are non-membrane active, internalize and have intracellular targets. Antimicrobial antisense agents such as peptide nucleic acids (PNA) and phosphorodiamidate morpholino oligomers (PMO), show great promise as novel antibacterial agents, killing bacteria by inhibiting translation of essential target gene transcripts. However, naked PNA and PMO are unable to translocate across the cell envelope of bacteria, to reach their target in the cytosol, and are conjugated to bacteria penetrating peptides (BPP) for cytosolic delivery. Here, we discuss how non-lytic AMP and BPP-PMO/PNA conjugates translocate across the cytoplasmic membrane via receptor-mediated transport, such as the cytoplasmic membrane transporters SbmA, MdtM/YjiL, and/or YgdD, or via a less well described autonomous process.

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.

Toward an understanding of tree frog (Hyla japonica) for predator deterrence

Gene-encoded peptides with distinct potent bioactivities enable several animals to take advantage of fierce interspecific interaction, as seen in the skin secretion of amphibians. Unlike, most amphibian species that frequently switches terrestrial-aquatic habitats and hides easily from terrestrial predators, tree frogs of small body size are considered as the vulnerable prey in the arboreal habitat. Here, we show the structural and functional diversity of peptide families based on the skin transcriptome of Hyla japonica, which has evolved to be wrapped as an efficient chemical toolkit for defensive use in arboreal habitat. Generally, the presence of antimicrobial peptide and proteinase inhibitor families reveals the functional consistency of Hyla japonica skin compared to other amphibian species. Furthermore, we found that Anntoxin-like neurotoxins with high expression levels are species-specific in tree frogs. Interestingly, derivatives in the Anntoxin-like family exhibit multiple evolutionary traits in modifying the copy number, folding type, and three-dimensional architecture, which are considered essential for targeting the ion channels of terrestrial predators. Together, our study not only reveals the peptide diversity in the skin secretion of H. japonica, but also draws insights into the predator-deterring strategy for coping with arboreal habitat.

Antimicrobial Peptides and Proteins: From Nature's Reservoir to the Laboratory and Beyond

Rapid rise of antimicrobial resistance against conventional antimicrobials, resurgence of multidrug resistant microbes and the slowdown in the development of new classes of antimicrobials, necessitates the urgent development of alternate classes of therapeutic molecules. Antimicrobial peptides (AMPs) are small proteins present in different lifeforms in nature that provide defense against microbial infections. They have been effective components of the host defense system for a very long time. The fact that the development of resistance by the microbes against the AMPs is relatively slower or delayed compared to that against the conventional antibiotics, makes them prospective alternative therapeutics of the future. Several thousands of AMPs have been isolated from various natural sources like microorganisms, plants, insects, crustaceans, animals, humans, etc. to date. However, only a few of them have been translated commercially to the market so far. This is because of some inherent drawbacks of the naturally obtained AMPs like 1) short half-life owing to the susceptibility to protease degradation, 2) inactivity at physiological salt concentrations, 3) cytotoxicity to host cells, 4) lack of appropriate strategies for sustained and targeted delivery of the AMPs. This has led to a surge of interest in the development of synthetic AMPs which would retain or improve the antimicrobial potency along with circumventing the disadvantages of the natural analogs. The development of synthetic AMPs is inspired by natural designs and sequences and strengthened by the fusion with various synthetic elements. Generation of the synthetic designs are based on various strategies like sequence truncation, mutation, cyclization and introduction of unnatural amino acids and synthons. In this review, we have described some of the AMPs isolated from the vast repertoire of natural sources, and subsequently described the various synthetic designs that have been developed based on the templates of natural AMPs or from de novo design to make commercially viable therapeutics of the future. This review entails the journey of the AMPs from their natural sources to the laboratory.

Enhanced Synergism and Mechanism of Action Studies of Synthetic Antimicrobial Metallopeptides

Antimicrobial peptides (AMPs) are found throughout most kingdoms of life, are an important part of host immunity, and have been shown to act synergistically in various organisms to ameliorate bacterial infections. Herein, we report the synergistic behavior observed between two AMPs, Sub5 and CP10A, against E. coli. In addition, enhanced synergistic activity against E. coli and MRSA 43300 for two derivatives of Sub5, extended with the amino-terminal copper and nickel (ATCUN) binding motif, is observed when dosed together with CP10A, while displaying little cytotoxicity towards human dermal fibroblasts. All three combinations of peptides co-localized within bacterial cells as evidenced by fluorescence confocal microscopy. Investigations into the mechanism of synergy shows that all peptides indirectly damage DNA within cells, while only the ATCUN derivatives can oxidize phospholipids. Combinations of peptides were also shown to upregulate the concentration of reactive oxygen species within both E. coli and MRSA 43300. These results suggest that the production of reactive oxygen species is an important aspect mechanistically and further highlights the potential of these metallopeptides to aid in the treatment of antibiotic-resistant infections.

Antimicrobial Peptides and Copper(II) Ions: Novel Therapeutic Opportunities

The emergence of new pathogens and multidrug resistant bacteria is an important public health issue that requires the development of novel classes of antibiotics. Antimicrobial peptides (AMPs) are a promising platform with great potential for the identification of new lead compounds that can combat the aforementioned pathogens due to their broad-spectrum antimicrobial activity and relatively low rate of resistance emergence. AMPs of multicellular organisms made their debut four decades ago thanks to ingenious researchers who asked simple questions about the resistance to bacterial infections of insects. Questions such as "Do fruit flies ever get sick?", combined with pioneering studies, have led to an understanding of AMPs as universal weapons of the immune system. This review focuses on a subclass of AMPs that feature a metal binding motif known as the amino terminal copper and nickel (ATCUN) motif. One of the metal-based strategies of hosts facing a pathogen, it includes wielding the inherent toxicity of copper and deliberately trafficking this metal ion into sites of infection. The sudden increase in the concentration of copper ions in the presence of ATCUN-containing AMPs (ATCUN-AMPs) likely results in a synergistic interaction. Herein, we examine common structural features in ATCUN-AMPs that exist across species, and we highlight unique features that deserve additional attention. We also present the current state of knowledge about the molecular mechanisms behind their antimicrobial activity and the methods available to study this promising class of AMPs.

Cryptic Host Defense Peptides: Multifaceted Activity and Prospects for Medicinal Chemistry

Host defense peptides (HDPs) comprise a heterogeneous group of evolutionarily conserved and biologically active small molecules that are produced by different organisms. HDPs are widely researched because they often have multiple biological activities, for example antimicrobial, immunomodulatory and anticancer activity. In this context, in this review we focus on cryptic HDPs, molecules derived specifically from proteolytic processing of endogenous precursor proteins. Here, we explore the biological activity of such molecules and we further discuss the development of optimized sequences based on these natural cryptic HDPs. In addition, we present clinical-phase studies of cryptic HDPs (natural or optimized), and point out the possible applicability of these molecules in medicinal chemistry.

Designed Metal-ATCUN Derivatives: Redox- and Non-redox-Based Applications Relevant for Chemistry, Biology, and Medicine

The designed "ATCUN" motif (amino-terminal copper and nickel binding site) is a replica of naturally occurring ATCUN site found in many proteins/peptides, and an attractive platform for multiple applications, which include nucleases, proteases, spectroscopic probes, imaging, and small molecule activation. ATCUN motifs are engineered at periphery by conjugation to recombinant proteins, peptides, fluorophores, or recognition domains through chemically or genetically, fulfilling the needs of various biological relevance and a wide range of practical usages. This chemistry has witnessed significant growth over the last few decades and several interesting ATCUN derivatives have been described. The redox role of the ATCUN moieties is also an important aspect to be considered. The redox potential of designed M-ATCUN derivatives is modulated by judicious choice of amino acid (including stereochemistry, charge, and position) that ultimately leads to the catalytic efficiency. In this context, a wide range of M-ATCUN derivatives have been designed purposefully for various redox- and non-redox-based applications, including spectroscopic probes, target-based catalytic metallodrugs, inhibition of amyloid-β toxicity, and telomere shortening, enzyme inactivation, biomolecules stitching or modification, next-generation antibiotic, and small molecule activation.

Antimicrobial Secretions of Toads (Anura, Bufonidae): Bioactive Extracts and Isolated Compounds against Human Pathogens

Species of the family Bufonidae, better known as true toads, are widespread and produce bioactive substances in the secretions obtained from specialized skin macroglands. Some true toads have been employed as a folk remedy to treat infectious diseases caused by microbial pathogens. Recent publications based on in silico analysis highlighted the Bufonidae as promising sources of antimicrobial peptides. A review of the literature reveals that Bufonidae skin secretion extracts show inhibitory activity in vitro against clinical isolates of bacteria, resistant and standard strains of bacterial, and fungal and parasitic human pathogens. Secondary metabolites belonging to the classes of alkaloids, bufadienolides, and peptides with antimicrobial activity have been isolated from species of the genera Bufo, Bufotes, Duttaphrynus, and Rhinella. Additionally, some antimicrobial extracts and purified compounds display low cytotoxicity against mammal cells.

Evaluation of Antimicrobial Activity of Buforin I and Nisin and Synergistic Effect of the Combination of them as a Novel Antimicrobial Preservative

One of the most effective methods for increasing the antimicrobial activity of a substance is to combine it with one or more other antimicrobial agents. The aim of the present study was to evaluate the antimicrobial effect of buforin I and nisin alone and investigate the synergistic action of these compounds against the most important food spoilage microorganisms in clouding B. subtilis, S. epidermidis, L. innocua, E. coli, S. Enteritidis, A. oryzae, R. glutinis and G. candidum. The results of MIC and MBC/MFC examinations showed that buforin I had higher antimicrobial activity than nisin on all the microbial strains used in this study (p≤0.5). E.coli was the most resistant to both antimicrobial agents, while Listeria innocua and Staphylococcus epidermidis were the most sensitive to nisin and buforin I, respectively. The results of synergistic interaction between buforin I and nisin indicated that the combination of buforin I and nisin on B. subtilis, S. epidermidis and A. oryzae showed synergistic effect, while it had no effect on S. Enteritidis and Geotrichum candidum. The combination of buforin I and nisin showed partial synergistic effect on Listeria innocua, Escherichia coli, Rhodotorula glutinis. Assessment of viability of the microorganisms under the antimicrobial agents alone and in combination with each other at MICs and FICs indicated that use of these antimicrobial agents in combination enhances antimicrobial activity at lower concentrations of both agents. The present study investigated the antimicrobial properties of buforin I against food spoilage microorganisms for the first time and suggests that its use alone or in combination with nisin may provide a clear horizon for the application of antimicrobial peptides as natural preservatives. Thus, the combination of antimicrobial peptides and traditional antimicrobial food preservative could be a promising option for the prevention of contamination, spoilage, and infestation of food and beverage products.

A histone H2A-derived antimicrobial peptide, Hipposin from mangrove whip ray, Himantura walga: Molecular and functional characterisation

Antimicrobial peptides (AMPs) are biologically dynamic molecules produced by all type of organisms as a fundamental component of their innate immune system. The present study deals with the identification of a histone H2A-derived antimicrobial peptide, Hipposin from mangrove whip ray, Himantura walga. A 243 base pair fragment encoding 81 amino acid residues amplified from complementary DNA was identified as Hipposin and termed as Hw-Hip. Homologous analysis showed that Hw-Hip belongs to the Histone H2A superfamily and shares sequence identity with other histone-derived AMPs from fishes. Phylogenetic analysis of Hw-Hip displayed clustering with the fish H2A histones. Secondary structure analysis showed the presence of three α-helices and four random coils with a prominent proline hinge. The physicochemical properties of Hw-Hip are in agreement with the properties of antimicrobial peptides. A 39-mer active peptide sequence was released by proteolytic cleavage in silico. Functional characterisation of active peptide in silico revealed antibacterial, anticancer and antibiofilm activities making Hw-Hip a promising candidate for further exploration.

Putative Antimicrobial Peptides of the Posterior Salivary Glands from the Cephalopod Octopus vulgaris Revealed by Exploring a Composite Protein Database

Cephalopods, successful predators, can use a mixture of substances to subdue their prey, becoming interesting sources of bioactive compounds. In addition to neurotoxins and enzymes, the presence of antimicrobial compounds has been reported. Recently, the transcriptome and the whole proteome of the Octopus vulgaris salivary apparatus were released, but the role of some compounds—e.g., histones, antimicrobial peptides (AMPs), and toxins—remains unclear. Herein, we profiled the proteome of the posterior salivary glands (PSGs) of O. vulgaris using two sample preparation protocols combined with a shotgun-proteomics approach. Protein identification was performed against a composite database comprising data from the UniProtKB, all transcriptomes available from the cephalopods’ PSGs, and a comprehensive non-redundant AMPs database. Out of the 10,075 proteins clustered in 1868 protein groups, 90 clusters corresponded to venom protein toxin families. Additionally, we detected putative AMPs clustered with histones previously found as abundant proteins in the saliva of O. vulgaris. Some of these histones, such as H2A and H2B, are involved in systemic inflammatory responses and their antimicrobial effects have been demonstrated. These results not only confirm the production of enzymes and toxins by the O. vulgaris PSGs but also suggest their involvement in the first line of defense against microbes.

Quantitative proteomic analysis in serum of Takifugu rubripes infected with Cryptocaryon irritans

Cryptocaryon irritans can cause cryptocaryonosis (white spot disease) in marine fish but the pathogenesis of the disease is unclear. In this work, we used high-throughput proteomics to identify differentially expressed proteins in the serum of Takifugu rubripes challenged with C. irritans. By using quantitative proteomic assays combined with Tandem Mass Tag-labeled quantitative proteomic analysis, we identified a total of 2088 differentially abundant proteins (1706 proteins were quantified, p < 0.05, fold-change threshold ≥ 2), including 21 up-regulated and 44 down-regulated. Combined with STRING-based functional analysis, we ultimately obtained eight proteins including glucokinase-like, integrin beta-1-like isoform X2, H4, H2A.V, histone H1-like, histone H2AX-like, histone H2B 1/2-like and myosin-9 isoform X1, which could be considered as potential biomarkers for T. rubripes immune responses. Eight proteins that were selected to validate significant differentially expressed genes at the proteomic level were consistent with qPCR at the transcriptomic level. The proteins identified in our work may serve as candidates for elucidating the molecular mechanism of cryptocaryonosis in T. rubripes. Our collective findings could provide new insights into searching for disease-specific targets and biomarkers, which may be effective indicators of C. irritans infection in T. rubripes.

Antimicrobial Activities of Different Fractions from Mucus of the Garden Snail Cornu aspersum

Natural products have long played a major role in medicine and science. The garden snail Cornu aspersum is a rich source of biologically active natural substances that might be an important source for new drugs to treat human disease. Based on our previous studies, nine fractions containing compounds with Mw <3 kDa; <10 kDa; <20 kDa; >20 kDa; >30 kDa>50 kDa and between 3 and 5 kDa; 5 and 10 kDa; and 10 and 30 kDa were purified from the mucus of C. aspersum and analyzed by tandem mass spectrometry (MALDI-TOF/TOF). Seventeen novel peptides with potential antibacterial activity were identified by de novo MS/MS sequencing using tandem mass spectrometry. The different fractions were tested for antibacterial activity against Gram─ (Pseudomonas aureofaciens and Escherichia coli) and Gram+ (Brevibacillus laterosporus) bacterial strains as well the anaerobic bacterium Clostridium perfringens. These results revealed that the peptide fractions exhibit a predominant antibacterial activity against B. laterosporus; the fraction with Mw 10-30 kDa against E. coli; another peptide fraction <20 kDa against P. aureofaciens; and the protein fraction >20 kDa against the bacterial strain C. perfringens. The discovery of new antimicrobial peptides (AMPs) from natural sources is of great importance for public health due to the AMPs' effective antimicrobial activities and low resistance rates.

Design, Engineering and Discovery of Novel α-Helical and β-Boomerang Antimicrobial Peptides against Drug Resistant Bacteria

In an era where the pipeline of new antibiotic development is drying up, the continuous rise of multi-drug resistant (MDR) and extensively drug resistant (XDR) bacteria are genuine threats to human health. Although antimicrobial peptides (AMPs) may serve as promising leads against drug resistant bacteria, only a few AMPs are in advanced clinical trials. The limitations of AMPs, namely their low in vivo activity, toxicity, and poor bioavailability, need to be addressed. Here, we review engineering of frog derived short α-helical AMPs (aurein, temporins) and lipopolysaccharide (LPS) binding designed β-boomerang AMPs for further development. The discovery of novel cell selective AMPs from the human proprotein convertase furin is also discussed.

Artificial Metalloenzymes: Recent Developments and Innovations in Bioinorganic Catalysis

Cellular life is orchestrated by the biochemical components of cells that include nucleic acids, lipids, carbohydrates, proteins, and cofactors such as metabolites and metals, all of which coalesce and function synchronously within the cell. Metalloenzymes allow for such complex chemical processes, as they catalyze a myriad of biochemical reactions both efficiently and selectively, where the metal cofactor provides additional functionality to promote reactivity not readily achieved in their absence. While the past 60 years have yielded considerable insight on how enzymes catalyze these reactions, a need to engineer and develop artificial metalloenzymes has been driven not only by industrial and therapeutic needs, but also by innate human curiosity. The design of miniature enzymes, both rationally and through serendipity, using both organic and inorganic building blocks has been explored by many scientists over the years and significant progress has been made. Herein, recent developments over the past 5 years in areas that have not been recently reviewed are summarized, and prospects for future research in these areas are addressed.