Identification and characterization of antimicrobial peptides from skin of Amolops ricketti (Anura: Ranidae)

Antimicrobial peptides (AMPs) from microalgae as an alternative to conventional antibiotics in aquaculture

The excessive use of conventional antibiotics has resulted in significant aquatic pollution and a concerning surge in drug-resistant bacteria. Efforts have been consolidated to explore and develop environmentally friendly antimicrobial alternatives to mitigate the imminent threat posed by multi-resistant pathogens. Antimicrobial peptides (AMPs) have gained prominence due to their low propensity to induce bacterial resistance, attributed to their multiple mechanisms of action and synergistic effects. Microalgae, particularly cyanobacteria, have emerged as promising alternatives with antibiotic potential to address these challenges. The aim of this review is to present some AMPs extracted from microalgae, emphasizing their activity against common pathogens and elucidating their mechanisms of action, as well as their potential application in the aquaculture industry. Likewise, the biosynthesis, advantages and disadvantages of the use of AMPs are described. Currently, biotechnology tolls are used to enhance the action of these peptides, such as genetically modified microalgae and recombinant proteins. Cyanobacteria are also mentioned as major producers of peptides, among them, the genus Lyngbya is described as the most important producer of bioactive peptides with potential therapeutic use. The majority of cyanobacterial AMPs are of the cyclic type, meaning that they have cysteine and disulfide bridges, thanks to this, their greater antimicrobial activity and selectivity. Likewise, we found that large hydrophobic aromatic amino acid residues increase specificity, and improve antibacterial efficacy. However, based on the results of this review, it is possible to highlight that while microalgae show potential as a source of AMPs, further research in this field is necessary to achieve safe and competitive production. Therefore, the data presented here can aid in the selection of microalgal species, peptide structures, and target bacteria, with the goal of establishing biotechnological platforms for aquaculture applications.

Brevinin-2PN, an antimicrobial peptide identified from dark-spotted frog (Pelophylax nigromaculatus), exhibits wound-healing activity

Brevinins exhibit a wide range of structural features and strong biological activities. Brevinin-2, derived from several amphibians, has shown antimicrobial activities. However, little is known about the wound-healing activity of brevinin-2. In this study, brevinin-2 cDNA was identified from the skin transcriptome of the dark-spotted frog (Pelophylax nigromaculatus) and it comprises a signal peptide, a propeptide, and a mature peptide. Sequence alignment with brevinin-2 derived from other amphibians showed variability of the mature peptide, and the presence of a C-terminal cyclic heptapeptide domain (Cys-Lys-Xaa4-Cys) in the mature peptide. Dark-spotted frog brevinin-2 belonged to the brevinin-2 cluster and was closely related to brevinin-2HB1 from Pelophylax hubeiensis. Synthetic dark-spotted frog brevinin-2 mature peptide (brevinin-2PN) exhibited antibacterial activity against several pathogens by destroying cell membrane integrity and hydrolysis of genomic DNA. Brevinin-2PN exhibited significant wound-healing activity by accelerating the healing of human skin fibroblast cell scratches, influencing cell migration, and stimulating gene expression of growth factors.

Development and characterization of twelve microsatellite loci for Amolops ricketti using next-generation sequencing

Amphibian populations have decreased dramatically because of human disturbance. To better conserve and manage native or wild populations of Amolops ricketti, 12 novel microsatellite loci were developed using high-throughput sequencing. The number of alleles ranged from 2 to 19, with an average of 7.67 alleles per locus. The observed and expected heterozygosity ranged from 0.42 to 1.00 (average 0.81) and from 0.51 to 0.95 (average 0.76), respectively. The polymorphism information content per locus ranged from 0.38 to 0.92 (average 0.69). These polymorphic microsatellite markers will contribute to the assessment of population structure, gene flow and genetic differentiation in A. ricketti.

Evaluating the Bioactivity of a Novel Broad-Spectrum Antimicrobial Peptide Brevinin-1GHa from the Frog Skin Secretion of Hylarana guentheri and Its Analogues

Many antimicrobial peptides (AMPs) have been identified from the skin secretion of the frog Hylarana guentheri (H.guentheri), including Temporin, Brevinin-1, and Brevinin-2. In this study, an antimicrobial peptide named Brevinin-1GHa was identified for the first time by using ‘shotgun’ cloning. The primary structure was also confirmed through mass spectral analysis of the skin secretion purified by reversed-phase high-performance liquid chromatography (RP-HPLC). There was a Rana-box (CKISKKC) in the C-terminal of Brevinin-1GHa, which formed an intra-disulfide bridge. To detect the significance of Rana-box and reduce the hemolytic activity, we chemically synthesized Brevinin-1GHb (without Rana-box) and Brevinin-1GHc (Rana-box in central position). Brevinin-1GHa exhibited a strong and broad-spectrum antimicrobial activity against seven microorganisms, while Brevinin-1GHb only inhibited the growth of Staphylococcus aureus (S. aureus), which indicates Rana-box was necessary for the antimicrobial activity of Brevinin-1GHa. The results of Brevinin-1GHc suggested transferring Rana-box to the central position could reduce the hemolytic activity, but the antimicrobial activity also declined. Additionally, Brevinin-1GHa demonstrated the capability of permeating cell membrane and eliminating biofilm of S. aureus, Escherichia coli (E. coli), and Candida albicans (C. albicans). The discovery of this research may provide some novel insights into natural antimicrobial drug design.

Identification and functional analyses of novel antioxidant peptides and antimicrobial peptides from skin secretions of four East Asian frog species

In the present study, we identified 50 peptides that are classified into 21 peptide families with antioxidant and/or antimicrobial activity from Amolops daiyunensis, Pelophylax hubeiensis, Hylarana maosuoensis and Nanorana pleskei, which belong to four different genera in the Ranidae and Dicroglossidae families. These four frog species were found for the first time to express antioxidant peptides (AOPs) and antimicrobial peptides (AMPs). These peptides include seven newly discovered families daiyunin-1, daiyunin-2, daiyunin-3, maosonensis-1MS1, pleskein-1, pleskein-2, and pleskein-3. Antioxidant and antimicrobial activity assays showed that some of these peptides have good biological activities. For example, at a concentration of 50 μM, nigroain-B-MS1, and nigroain-C-MS1 both exhibited relatively strong 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonicacid) (ABTS) free radical scavenging ability, with eradication rates of 99.7% and 68.3% (nigroain-B-MS1), and 99.8% and 58.3% (nigroain-C-MS1), respectively. These peptides are potential candidates for the development of novel antioxidant or AMP preparations.

Host Defense Peptides from Asian Frogs as Potential Clinical Therapies

Host defense peptides (HDPs) are currently major focal points of medical research as infectious microbes are gaining resistance to existing drugs. They are effective against multi-drug resistant pathogens due to their unique primary target, biological membranes, and their peculiar mode of action. Even though HDPs from 60 Asian frog species belonging to 15 genera have been characterized, research into these peptides is at a very early stage. The purpose of this review is to showcase the status of peptide research in Asia. Here we provide a summary of HDPs from Asian frogs.

Identification and characterization of an antimicrobial peptide of Hypsiboas semilineatus (Spix, 1824) (Amphibia, Hylidae)

The multidrug-resistant bacteria have become a serious problem to public health. In this scenery the antimicrobial peptides (AMPs) derived from animals and plants emerge as a novel therapeutic modality, substituting or in addition to the conventional antimicrobial. The anurans are one of the richest natural sources of AMPs. In this work several cycles of cDNA cloning of the skin of the Brazilian treefrog Hypsiboas semilineatus led to isolation of a precursor sequence that encodes a new AMP. The sequence comprises a 27 residue signal peptide, followed by an acidic intervening sequence that ends in the mature peptide at the carboxy terminal. The AMP, named Hs-1, has 20 amino acids residues, mostly arranged in an alpha helix and with a molecular weight of 2144.6 Da. The chemically synthesized Hs-1 showed an antimicrobial activity against all Gram-positive bacteria tested, with a range of 11-46 μM, but it did not show any effect against Gram-negative bacteria, which suggest that Hs-1 may have a selective action for Gram-positive bacteria. The effects of Hs-1 on bacterial cells were also demonstrated by transmission electron microscopy. Hs-1 is the first AMP to be described from H. semilineatus.

Characterization of antibacterial and hemolytic activity of synthetic pandinin 2 variants and their inhibition against Mycobacterium tuberculosis

The contention and treatment of Mycobacterium tuberculosis and other bacteria that cause infectious diseases require the use of new type of antibiotics. Pandinin 2 (Pin2) is a scorpion venom antimicrobial peptide highly hemolytic that has a central proline residue. This residue forms a structural “kink” linked to its pore-forming activity towards human erythrocytes. In this work, the residue Pro14 of Pin2 was both substituted and flanked using glycine residues (P14G and P14GPG) based on the low hemolytic activities of antimicrobial peptides with structural motifs Gly and GlyProGly such as magainin 2 and ponericin G1, respectively. The two Pin2 variants showed antimicrobial activity against E. coli, S. aureus, and M. tuberculosis. However, Pin2 [GPG] was less hemolytic (30%) than that of Pin2 [G] variant. In addition, based on the primary structure of Pin2 [G] and Pin2 [GPG], two short peptide variants were designed and chemically synthesized keeping attention to their physicochemical properties such as hydrophobicity and propensity to adopt alpha-helical conformations. The aim to design these two short antimicrobial peptides was to avoid the drawback cost associated to the synthesis of peptides with large sequences. The short Pin2 variants named Pin2 [14] and Pin2 [17] showed antibiotic activity against E. coli and M. tuberculosis. Besides, Pin2 [14] presented only 25% of hemolysis toward human erythrocytes at concentrations as high as 100 µM, while the peptide Pin2 [17] did not show any hemolytic effect at the same concentration. Furthermore, these short antimicrobial peptides had better activity at molar concentrations against multidrug resistance M. tuberculosis than that of the conventional antibiotics ethambutol, isoniazid and rifampicin. Therefore, Pin2 [14] and Pin2 [17] have the potential to be used as an alternative antibiotics and anti-tuberculosis agents with reduced hemolytic effects.

Peptidomic analysis of antimicrobial peptides in skin secretions of Amolops mantzorum

Amphibian skin secretions contain abundant bioactive peptides that are valuable natural resources for human beings. However, many amphibians are disappearing from the world, making relevant scientific studies even more important. In this study, 24 cDNA sequences encoding antimicrobial peptide (AMP) precursors were initially cloned by screening a cDNA library derived from the skin of the Sichuan torrent frog, Amolops mantzorum. Eighteen mature AMPs belonging to 11 different families were deduced from these cDNA clones. Biological function was confirmed in each family of these AMPs. Some of them were purified from the skin secretions, and their molecular structures were determined by Edman degradation. Liquid chromatography in conjunction with tandem mass spectrometry (LC-MS/MS)-based peptidomics was used to further confirm the actual presence and characteristics of mature AMPs in the skin secretions of A. mantzorum. Incomplete tryptic digestion and gas-phase fractionation (GPF) analysis were used to increase the peptidome coverage and reproducibility of peptide ion selection.

An overview of Brevinin superfamily: structure, function and clinical perspectives

Antimicrobial peptides are the backbone of first-line defense against various microorganisms in the animal kingdom. Thus, not surprisingly, they are gaining attention in the science and medical fields as a rich repository of new pro-drugs. Below, we focus our attention on the Brevinin family of anuran peptides. While most of them show strong antibacterial activities, some, e.g. Brevinin-2R, appear to be promising anticancer molecules, exhibiting better a therapeutic window than widely-use anticancer drugs like doxorubicin. We briefly introduce the field, followed by highlighting the promising therapeutic properties of Brevinins. Next, we provide information about the cloning and phylogenetic aspects of Brevinin genes. In the final paragraphs of this chapter, we discuss possible large-scale production methods of Brevinins, giving examples of some systems that are already in use. Towards the end, we discuss various means of modification of biologic properties of Brevinins, either by chemical modifications or by amino acid substitution and sequence rearrangements. In this context, also other unique properties of Brevinins are briefly mentioned. Finally, we discuss the future of the Brevinin field, particularly highlighting yet to be answered biologic questions, like for example presumed anti-viral and antitumor activities of Brevinin family members.

Characterization of diverse antimicrobial peptides in skin secretions of Chungan torrent frog Amolops chunganensis

We have cloned, synthesized, and characterized 11 novel antimicrobial peptides from a skin derived cDNA library of the Chungan torrent frog, Amolops chunganensis. Seven of the 11 antimicrobial peptides were present in authentic A. chunganensis skin secretions. Sequence analysis indicated that the 11 peptides belonged to the temporin, esculentin-2, palustrin-2, brevinin-1, and brevinin-2 families. The peptides displayed potent antimicrobial activities against several strains of microorganisms. One peptide, brevinin-1CG5, demonstrated antimicrobial activity against all tested Gram-positive and Gram-negative bacteria and fungi, and showed high antimicrobial potency (MIC=0.6 μM) against Gram-positive bacterium Rhodococcus rhodochrous. Some peptides also demonstrated weak hemolytic activity against human erythrocytes in vitro. Phylogenetic analysis based on the amino acid sequences of brevinin-1, brevinin-2, and esculentin-2 peptides from family Ranidae confirmed that the current taxonomic status of A. chunganensis is correct.