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

Cathelicidin-HG Alleviates Sepsis-Induced Platelet Dysfunction by Inhibiting GPVI-Mediated Platelet Activation

Platelet activation contributes to sepsis development, leading to microthrombosis and increased inflammation, which results in disseminated intravascular coagulation and multiple organ dysfunction. Although Cathelicidin can alleviate sepsis, its role in sepsis regulation remains largely unexplored. In this study, we identified Cath-HG, a novel Cathelicidin from Hylarana guentheri skin, and analyzed its structure using nuclear magnetic resonance spectroscopy. The modulatory effect of Cath-HG on the symptoms of mice with sepsis induced by cecal ligation and puncture was evaluated in vivo, and the platelet count, degree of organ damage, and microthrombosis were measured. The antiplatelet aggregation activity of Cath-HG was studied in vitro, and its target was verified. Finally, we further investigated whether Cath-HG could regulate thrombosis in vivo in a FeCl3 injury-induced carotid artery model. The results showed that Cath-HG exhibited an α-helical structure in sodium dodecyl sulfate solution and effectively reduced organ inflammation and damage, improving survival in septic mice. It alleviated sepsis-induced thrombocytopenia and microthrombosis. In vitro, Cath-HG specifically inhibited collagen-induced platelet aggregation and modulated glycoprotein VI (GPVI) signaling pathways. Dot blotting, enzyme-linked immunosorbent assay, and pull-down experiments confirmed GPVI as the target of Cath-HG. Molecular docking and amino acid residue truncations/mutations identified crucial sites of Cath-HG. These findings suggest that GPVI represents a promising therapeutic target for sepsis, and Cath-HG may serve as a potential treatment for sepsis-related thrombocytopenia and thrombotic events. Additionally, identifying Cath-HG as a GPVI inhibitor provides insights for developing novel antithrombotic therapies targeting platelet activation mediated by GPVI.

Exploration of the Antibacterial and Anti-Inflammatory Activity of a Novel Antimicrobial Peptide Brevinin-1BW

Antibiotic resistance has emerged as a grave threat to global public health, leading to an increasing number of treatment failures. Antimicrobial peptides (AMPs) are widely regarded as potential substitutes for traditional antibiotics since they are less likely to induce resistance when used. A novel AMP named Brevinin-1BW (FLPLLAGLAASFLPTIFCKISRKC) was obtained by the Research Center of Molecular Medicine of Yunnan Province from the skin of the Pelophylax nigromaculatus. Brevinia-1BW had effective inhibitory effects on Gram-positive bacteria, with a minimum inhibitory concentration (MIC) of 3.125 μg/mL against Enterococcus faecalis (ATCC 29212) and 6.25 μg/mL against both Staphylococcus aureus (ATCC 25923) and multidrug-resistant Staphylococcus aureus (ATCC 29213) but had weaker inhibitory effects on Gram-negative bacteria, with a MIC of ≥100 μg/mL. Studies using scanning electron microscopy (SEM) and flow cytometry have revealed that it exerts its antibacterial activity by disrupting bacterial membranes. Additionally, it possesses strong biofilm inhibitory and eradication activities as well as significant lipopolysaccharide (LPS)-binding activity. Furthermore, Brevinin-1BW has shown a significant anti-inflammatory effect in LPS-treated RAW264.7 cells. In conclusion, Brevinin-1BW is anticipated to be a promising clinical agent with potent anti-Gram-positive bacterial and anti-inflammatory properties.

Discovery and analysis of a novel antimicrobial peptide B1AW from the skin secretion of Amolops wuyiensis and improving the membrane-binding affinity through the construction of the lysine-introduced analogue

In the development and study of antimicrobial peptides (AMPs), researchers have kept a watchful eye on peptides from the brevinin family because of their extensive antimicrobial activities and anticancer potency. In this study, a novel brevinin peptide was isolated from the skin secretions of the Wuyi torrent frog, Amolops wuyiensis (A. wuyiensisi), named B1AW (FLPLLAGLAANFLPQIICKIARKC). B1AW displayed anti-bacterial activity against Gram-positive bacteria Staphylococcus aureus (S. aureus), methicillin-resistant Staphylococcus aureus (MRSA), and Enterococcus faecalis (E. faecalis). B1AW-K was designed to broaden the antimicrobial spectrum of B1AW. The introduction of a lysine residue generated an AMP with enhanced broad-spectrum antibacterial activity. It also displayed the ability to inhibit the growth of human prostatic cancer PC-3, non-small lung cancer H838, and glioblastoma cancer U251MG cell lines. In molecular dynamic (MD) simulations, B1AW-K had a faster approach and adsorption to the anionic membrane than B1AW. Therefore, B1AW-K was considered a drug prototype with a dual effect, which deserves further clinical investigation and validation.

Bioactive compounds: a goldmine for defining new strategies against pathogenic bacterial biofilms?

Most human infectious diseases are caused by microorganisms growing as biofilms. These three-dimensional self-organized communities are embedded in a dense matrix allowing microorganisms to persistently inhabit abiotic and biotic surfaces due to increased resistance to both antibiotics and effectors of the immune system. Consequently, there is an urgent need for novel strategies to control biofilm-associated infections. Natural products offer a vast array of chemical structures and possess a wide variety of biological properties; therefore, they have been and continue to be exploited in the search for potential biofilm inhibitors with a specific or multi-locus mechanism of action. This review provides an updated discussion of the major bioactive compounds isolated from several natural sources - such as plants, lichens, algae, microorganisms, animals, and humans - with the potential to inhibit biofilm formation and/or to disperse established biofilms by bacterial pathogens. Despite the very large number of bioactive products, their exact mechanism of action often remains to be clarified and, in some cases, the identity of the active molecule is still unknown. This knowledge gap should be filled thus allowing development of these products not only as novel drugs to combat bacterial biofilms, but also as antibiotic adjuvants to restore the therapeutic efficacy of current antibiotics.

SCMRSA: a New Approach for Identifying and Analyzing Anti-MRSA Peptides Using Estimated Propensity Scores of Dipeptides

Staphylococcus aureus is deemed to be one of the major causes of hospital and community-acquired infections, especially in methicillin-resistant S. aureus (MRSA) strains. Because antimicrobial peptides have captured attention as novel drug candidates due to their rapid and broad-spectrum antimicrobial activity, anti-MRSA peptides have emerged as potential therapeutics for the treatment of bacterial infections. Although experimental approaches can precisely identify anti-MRSA peptides, they are usually cost-ineffective and labor-intensive. Therefore, computational approaches that are able to identify and characterize anti-MRSA peptides by using sequence information are highly desirable. In this study, we present the first computational approach (termed SCMRSA) for identifying and characterizing anti-MRSA peptides by using sequence information without the use of 3D structural information. In SCMRSA, we employed an interpretable scoring card method (SCM) coupled with the estimated propensity scores of 400 dipeptides. Comparative experiments indicated that SCMRSA was more effective and could outperform several machine learning-based classifiers with an accuracy of 0.960 and Matthews correlation coefficient of 0.848 on the independent test data set. In addition, we employed the SCMRSA-derived propensity scores to provide a more in-depth explanation regarding the functional mechanisms of anti-MRSA peptides. Finally, in order to serve community-wide use of the proposed SCMRSA, we established a user-friendly webserver which can be accessed online at http://pmlabstack.pythonanywhere.com/SCMRSA. SCMRSA is anticipated to be an open-source and useful tool for screening and identifying novel anti-MRSA peptides for follow-up experimental studies.

Targeted Modification and Structure-Activity Study of GL-29, an Analogue of the Antimicrobial Peptide Palustrin-2ISb

Antimicrobial peptides (AMPs) are considered as promising antimicrobial agents due to their potent bioactivity. Palustrin-2 peptides were previously found to exhibit broad-spectrum antimicrobial activity with low haemolytic activity. Therefore, GL-29 was used as a template for further modification and study. Firstly, the truncated analogue, GL-22, was designed to examine the function of the ‘Rana box’, which was confirmed to have no impact on antimicrobial activity. The results of antimicrobial activity assessment against seven microorganisms demonstrated GL-22 to have a broad-spectrum antimicrobial activity, but weak potency against Candida albicans (C. albicans). These data were similar to those of GL-29, but GL-22 showed much lower haemolysis and lower cytotoxicity against HaCaT cells. Moreover, GL-22 exhibited potent in vivo activity at 4 × MIC against Staphylococcus aureus (S. aureus)-infected larvae. Several short analogues, from the C-terminus and N-terminus of GL-22, were modified to identify the shortest functional motif. However, the results demonstrated that the shorter peptides did not exhibit potent antimicrobial activity, and the factors that affect the bioactive potency of these short analogues need to be further studied.

Truncated analog Brevinin2-CE-N26V5K: Revelation the Augmentation of Antimicrobial Activity

Brevinin2-CE (B2CE), a natural peptide containing 37 amino acids, was first isolated from the skin secretions of the Chinese forest frog Rana chensinensis. B2CE shows good antibacterial activity. In this study, a series of B2CE analogs with differences in cationicity, α-helicity, hydrophobicity and amphipathic properties were designed through chain-length deletion and amino acid substitution. The most potent, nontoxic analog, B2CE-N26V5K, was identified by examination of its antibacterial activity, hemolytic activity, and stability under physiological conditions. The increased cationicity, hydrophobicity and more obvious hydrophilic and hydrophobic surface of B2CE-N26-N16WA18KG23K did not improve the antibacterial activity but increased the hemolytic activity of this modified peptide. The helicity might promote antibacterial activity for brevinin-2 peptides, as the 15-aa analogs with lower helicity show decreased potency against different test bacteria (approximately 2- to 72-fold) compared to B2CE-N26V5K. Additionally, the results indicated that the "Rana box" does not affect the antimicrobial activity of brevinin-2 peptides, as B2CE, B2CE-nonDS and B2CE-C31-37 S have similar strong inhibitory effects on both gram-positive and gram-negative bacteria. However, the "Rana box" does affect the hemolytic activity, as the HC₅₀ values of the 3 peptides range from 25 ~ 130 µM. Furthermore, B2CE-N26V5K caused obvious morphological alterations of the bacterial surfaces, as shown by atomic force microscopy. Additionally, B2CE-N26V5K exhibited strong membrane-disrupting activity when examined using the LIVE/DEAD Bac Light Bacterial Viability Kit. Thus, the antibacterial effect of B2CE-N26V5K on gram-negative and gram-positive bacteria may be caused by cell membrane attack. In conclusion, the excellent candidate B2CE-N26V5K was obtained and has application prospects as a novel anti-infective agent.

Synthetic peptides bioinspired in temporin-PTa with antibacterial and antibiofilm activity

Several antimicrobial peptides (AMPs) have been reported in amphibian toxins, as temporin-PTa from Hylarana picturata. The amino acid distribution within a helical structure of AMPs favors the design of new bioactive peptides. Therefore, this work reports the rational design of two new synthetic peptides denominated Hp-MAP1 and Hp-MAP2 derived from temporin-PTa. These peptides present an amphipathic helix with positive charges of +4 and +5, hydrophobic moment (<µH>) of 0.66 and 0.72 and hydrophobicity (<H>) of 0.49 and 0.41, respectively. Hp-MAP1 and Hp-MAP2 displayed in vitro activity against Gram-negative and Gram-positive bacteria from 2.8 to 92 µM, without presenting hemolytic effects. Molecular dynamics simulation suggested that the parent and designed temporin-like peptides lack structural stability in an aqueous solution. By contrast, α-helical structures were predicted in hydrophobic and anionic environments. Additionally, the peptides were simulated on mimetic membranes composed of anionic and neutral phospholipids 1,2-dipalmitoylsn-glycerol-3-phosphatidylglycerol (DPPG-anionic), 1,2-dipalmitoyl-sn-lyco-3 phosphatidylethanolamine (DPPE-neutral). When in contact with DPPG/DPPE (90:10) and DPPG/DPPE (50:50) temporin-PTa, Hp-MAP1 and Hp-MAP2 established interactions guided by hydrogen and saline bounds. Therefore, the findings described here reveal that the optimization of the amphipathic α-helical cationic peptides Hp-MAP1 and Hp-MAP2 enabled the generation of new synthetic antimicrobial agents to combat pathogenic microorganisms.

Membrane disruptive action of cationic anti-bacterial peptide B1CTcu3

A twenty-two-residue peptide Brevinin1 Clinotarsus curtipus-3 (B1CTcu3), identified from the skin secretion of frog Clinotarsus curtipes of the Western Ghats, exhibited a broad range of antibacterial activity against Gram-negative and Gram-positive bacteria, including the methicillin-resistant Staphylococcus aureus (MRSA). It showed anti-biofilm activity even at sub-Minimum Inhibitory Concentration (sub-MIC) against Pseudomonas aeruginosa and Staphylococcus aureus. Analysis of the scanning electron microscopic (SEM) images, confocal images, flow cytometric data and the effect of salt concentration on antibacterial potency suggests that the killing action of the peptide is through the membranolytic process. Single channel electric recording confirmed that the peptide elicited pores on the bacterial cell membrane as it induces a heterogeneous channel in the lipid bilayer.  It also showed cytotoxicity against MDA-MB-231 breast cancer cell with IC50 of 25µM. B1CTcu3 peptide could serve as the template for next-generation antibacterial agents, particularly against antibiotic resistant pathogenic bacteria.

[Antibacterial mechanism of Brevinin-2GHk, an antimicrobial peptide from Fejervarya limnocharis skin]

OBJECTIVE

To investigate the secondary structure, physicochemical properties and antibacterial activity of Brevinin- 2GHk (BR2GK), an antimicrobial peptide from frog skin, and explore its antibacterial mechanism.

METHODS

BR2GK was synthesized, purified with high performance liquid chromatography (HPLC) and identified using mass spectrometry. Circular dichroism was used to determine the secondary structure and physicochemical properties of BR2GK. Two-fold dilution method was used to determine the antibacterial activity of BR2GK, and its antibacterial mechanism was explored using laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM). The hemolytic activity of BR2GK was analyzed in red blood cells. Isothermal titration calorimetry (ITC) and surface plasmon resonance imaging (SPRi) were employed to detect the binding of BR2GK to lipopolysaccharide (LPS), and the antioxidant activity of BR2GK was evaluated using biochemical kits.

RESULTS

The synthesized BR2GK, with a purity exceeding 95% after purification, had the basic characteristics of cationic antimicrobial peptides. BR2GK consisted mainly of α-helical structure in SDS solution and exhibited a broad-spectrum antibacterial activity. Antibacterial activity assay showed that BR2GK had inhibitory and killing activity against a variety of strains with a minimum inhibitory concentration (MIC) of 2.76 μmol/L against Staphylococcus aureus. Observation with LSCM and SEM showed that BR2GK at an active concentration caused bacterial cell membrane damage, cell swelling, contraction, deformation, and massive exudation of intracellular contents without causing hemolysis. ITC showed that the binding affinity K_D of BR2GK to LPS was 18.2±0.8 μmol/L. The antioxidant test showed that BR2GK was capable of effectively scavenging NO, ABTS and DPPH.

CONCLUSION

BR2GK, as a broad-spectrum antibacterial peptide with also a strong antioxidant capacity, does not cause hemolysis and is capable of binding to LPS. BR2GK has an important value for future design and synthesis of antimicrobial peptides with stronger antibacterial activity and lower cytotoxicity.

Evaluation of antimicrobial and anticancer activities of three peptides identified from the skin secretion of Hylarana latouchii

The skins of frogs of the family Ranidae are particularly rich sources of biologically active peptides, among which antimicrobial peptides (AMPs) constitute the major portion. Some of these have attracted the interest of researchers because they possess both antimicrobial and anticancer activities. In this study, with 'shotgun' cloning and MS/MS fragmentation, three AMPs, homologues of family brevinin-1 (brevinin-1HL), and temporin (temporin-HLa and temporin-HLb), were discovered from the skin secretion of the broad-folded frog, Hylarana latouchii. They exhibited various degrees of antimicrobial and antibiofilm activities against test microorganisms and hemolysis on horse erythrocytes. It was found that they could induce bacteria death through disrupting cell membranes and binding to bacterial DNA. In addition, they also showed different potencies towards human cancer cell lines. The secondary structure and physicochemical properties of each peptide were investigated to preliminarily reveal their structure-activity relationships. Circular dichroism spectrometry showed that they all adopted a canonical α-helical conformation in membrane-mimetic solvents. Notably, the prepropeptide of brevinin-1HL from H. latouchii was highly identical to that of brevinin-1GHd from Hylarana guentheri, indicating a close relationship between these two species. Accordingly, this study provides candidates for the design of novel anti-infective and antineoplastic agents to fight multidrug-resistant bacteria and malignant tumors and also offers additional clues for the taxonomy of ranid frogs.

Bioevaluation and Targeted Modification of Temporin-FL From the Skin Secretion of Dark-Spotted Frog (Pelophylax nigromaculatus)

Bioactive proteins secreted by the granular glands of amphibian skin play a self-defensive role, and exhibit various bioactivities in vitro and in vivo. In light of the severity of the problem of antibiotic resistance for treating infections, many antimicrobial peptides (AMPs) have been developed and applied in clinical microbial treatments. We identified a naturally derived and potent antimicrobial peptide, temporin-FL, obtained from the skin secretion of Pelophylax nigromaculatus via “shotgun” cloning. Two truncated analogues of this peptide were chemically synthesized to explore their structural-functional relationships. The results of a functional evaluation showed that all of the tested AMPs were active against Gram-positive bacteria and fungi and demonstrated antibiofilm activity against methicillin-resistant Staphylococcus aureus (MRSA) but did not have an effect on Gram-negative bacteria. Moreover, temporin-FLa demonstrated a higher level of hydrophobicity and enhanced antimicrobial efficiency, as well as hemolytic activity and cell cytotoxicity than the parent peptide. Temporin-FLb, which evidenced significantly less α-helicity, was less potent against various microbes but exhibited lower cytotoxicity relating to mammalian cells. Both of the synthesized analogues possessed a higher therapeutic index than the original peptide. Moreover, the membrane permeability assay and the measuring membrane depolarization assay declared that temporin-FL and its analogues induced membrane fracture and depolarization; the quantitative biofilm formation assay and the observations of MRSA biofilms using scanning electron microscopy revealed that the AMPs caused biofilm disruption and blocked biofilm formation, the former experiments all confirming their antimicrobial and antibiofilm properties. Hence, the optimization of temporin-FL offers insights for the discovery of new drugs for treating MRSA infections.

Study on the Structure-Activity Relationship of an Antimicrobial Peptide, Brevinin-2GUb, from the Skin Secretion of Hylarana guentheri

Antimicrobial peptides (AMPs) are considered potential alternatives to antibiotics due to their advantages in solving antibiotic resistance. Brevinin-2GUb, which was extracted from the skin secretion of Hylarana guentheri, is a peptide with modest antimicrobial activity. Several analogues were designed to explore the structure–activity relationship and enhance its activity. In general, the Rana box is not an indispensable motif for the bioactivity of Brevinin-2GUb, and the first to the 19th amino acids at the N-terminal end are active fragments, such that shortening the peptide while maintaining its bioactivity is a promising strategy for the optimisation of peptides. Keeping a complete hydrophobic face and increasing the net charges are key factors for antimicrobial activity. With the increase of cationic charges, α-helical proportion, and amphipathicity, the activity of t-Brevinin-2GUb-6K (tB2U-6K), in combatting bacteria, drastically improved, especially against Gram-negative bacteria, and the peptide attained the capacity to kill clinical isolates and fungi as well, which made it possible to address some aspects of antibiotic resistance. Thus, peptide tB2U-6K, with potent antimicrobial activity against antibiotic-resistant bacteria, the capacity to inhibit the growth of biofilm, and low toxicity against normal cells, is of value to be further developed into an antimicrobial agent.

Antimicrobial Peptide Brevinin-1RL1 from Frog Skin Secretion Induces Apoptosis and Necrosis of Tumor Cells

Cancer has always been one of the most common malignant diseases in the world. Therefore, there is an urgent need to find potent agents with selective antitumor activity against cancer cells. It has been reported that antimicrobial peptides (AMPs) can selectively target tumor cells. In this study, we focused on the anti-tumor activity and mechanism of Brevivin-1RL1, a cationic α-helical AMP isolated from frog Rana limnocharis skin secretions. We found that Brevivin-1RL1 preferentially inhibits tumor cells rather than non-tumor cells with slight hemolytic activity. Cell viability assay demonstrated the intermolecular disulfide bridge contributes to the inhibitory activity of the peptide as the antitumor activity was abolished when the disulfide bridge reduced. Further mechanism studies revealed that both necrosis and apoptosis are involved in Brevivin-1RL1 mediated tumor cells death. Moreover, Brevivin-1RL1 induced extrinsic and mitochondria intrinsic apoptosis is caspases dependent, as the pan-caspase inhibitor z-VAD-FMK rescued Brevinin-1RL1 induced tumor cell proliferative inhibition. Immunohistology staining showed Brevivin-1RL1 mainly aggregated on the surface of the tumor cells. These results together suggested that Brevivin-1RL1 preferentially converges on the cancer cells to trigger necrosis and caspase-dependent apoptosis and Brevivin-1RL1 could be considered as a pharmacological candidate for further development as anti-cancer agent.

Brevinin-1GHd: a novel Hylarana guentheri skin secretion-derived Brevinin-1 type peptide with antimicrobial and anticancer therapeutic potential

Host-defense antimicrobial peptides (AMPs) from amphibians are usually considered as one of the most promising next-generation antibiotics because of their excellent antimicrobial properties and low cytotoxicity. In the present study, one novel Brevinin-1 type peptide, Brevinin-1GHd, was isolated and characterized from the skin secretion of the frog, Hylarana guentheri. Brevinin-1GHd was found to possess a wide range of antimicrobial activity through penetrating the bacterial membrane within a short time while showing low hemolysis at bactericidal concentrations, even against the resistant strains. It also inhibited and eradicated biofilms that are thought to be closely related to the rise in resistance. Meanwhile, Brevinin-1GHd exhibited wide-spectrum anti-proliferation activity toward human cancer lines. Taken together, these results indicate that Brevinin-1GHd with its excellent antimicrobial and anticancer activities is a promising candidate for a novel antibiotic agent, and study of its structure–activity relationships also provided a rational template for further research and peptide analog design.

Characterisation of a novel peptide, Brevinin-1H, from the skin secretion of Amolops hainanensis and rational design of several analogues

As drug-resistant bacteria have become a serious health problem and have caused thousands of deaths, finding new antibiotics has become an urgent research priority. A novel antimicrobial peptide, named Brevinin-1H, was identified in the skin secretion of Amolops hainanensis through 'shotgun' cloning. It has broad-spectrum antimicrobial activity against tested micro-organisms and has anticancer cell activity. To improve its bioactivity and decrease its cytotoxicity, two structural analogues-Brevinin-1Ha and Brevinin-1HY-were designed based on the secondary structure of the natural peptide. Brevinin-1HY, in which tyrosine substituted Pro¹¹ , had similar activity to the natural peptide against Gram-negative bacteria and cancer cells, but showed a dramatic increase in haemolytic activity and cytotoxicity at its minimum inhibitory concentration. Brevinin-1Ha, which transferred the Rana-box from the C-terminal to a central position, had significantly decreased haemolytic activity, but also in antimicrobial and anticancer activity. The present data suggest that increasing the proportion of α-helix structure in an AMP can increase its target micro-organism bioactivity to some extent.

Enhanced Antimicrobial Activity of N-Terminal Derivatives of a Novel Brevinin-1 Peptide from The Skin Secretion of Odorrana schmackeri

Antimicrobial peptides (AMPs) are promising therapeutic alternatives compared to conventional antibiotics for the treatment of drug-resistant bacterial infections. However, the application of the overwhelming majority of AMPs is limited because of the high toxicity and high manufacturing costs. Amphibian skin secretion has been proven to be a promising source for the discovery and development of novel AMPs. Herein, we discovered a novel AMP from the skin secretion of Odorrana schmackeri, and designed the analogues by altering the key factors, including conformation, net charge and amphipathicity, to generate short AMPs with enhanced therapeutic efficacy. All the peptides were chemically synthesised, followed by evaluating their biological activity, stability and cytotoxicity. OSd, OSe and OSf exhibited broad-spectrum antibacterial effects, especially OSf, which presented the highest therapeutic index for the tested bacteria. Moreover, these peptides displayed good stability. The results from scanning electron microscopy and transmission electron microscopy studies, indicated that brevinin-OS, OSd, OSe and OSf possessed rapid bactericidal ability by disturbing membrane permeability and causing the release of cytoplasmic contents. In addition, OSd, OSe and OSf dramatically decreased the mortality of waxworms acutely infected with MRSA. Taken together, these data suggested that a balance between positive charge, degrees of α-helicity and hydrophobicity, is necessary for maintaining antimicrobial activity, and these data successfully contributed to the design of short AMPs with significant bactericidal activity and cell selectivity.

Identification of new dermaseptins with self-assembly tendency: membrane disruption, biofilm eradication, and infected wound healing efficacy

Severe infections associated with antibiotic-resistant bacteria and biofilms have attracted increasing interest as these diseases are difficult to treat with current antibiotics. Typical cationic antimicrobial peptides dermaseptins are considered to be the most promising next-generation antibiotics because of their broad-spectrum antimicrobial activities and minor side effects. Two new dermaseptin peptides, DMS-PS1 and DMS-PS2, have been identified by "shotgun" molecular cloning of encoding cDNAs in the crude skin secretions of the waxy monkey tree frog, Phyllomedusa sauvagei. The mature peptide sequences predicted from the cloned cDNAs were separated from crude skin secretions and confirmed by mass spectrometry. Chemically synthetic replicates were assessed for various biological activities. Both dermaseptins were potently effective against a broad spectrum of microorganisms including antibiotic-resistant bacteria and displayed significant potency against gram-positive and gram-negative bacterial biofilms with low toxicity towards mammalian red blood cells. Remarkably, DMS-PS2 was effective against infections in murine skin caused by methicillin-resistant Staphylococcus aureus as a result of an induced wound. The actions of DMS-PS2 were with a membrane permeabilization mode. Overall, the data provided convincing evidence for the development of anti-infectious agents and/or biomaterials as a new therapeutic approach against bacterial infections. STATEMENT OF SIGNIFICANCE: Bacterial adhesion to biomaterials remains a major problem. Antimicrobial peptides (AMPs) are well-known components of the innate immune system that can be applied to overcome biofilm-associated infections. Cationic dermaseptin peptides showed significant broad-spectrum antimicrobial activities and activities against bacterial biofilms of persistent infections in association with weak toxicity for mammalian red blood cells. The membrane permeabilizing ability of DMS-PS2 was confirmed, and importantly, it demonstrated potent efficiency of the treatment of MRSA infected murine skin model. Furthermore, beyond our expectation, DMS-PS2 showed a self-aggregating parameter, indicating a promising potential for the use of immobilized AMPs in clinical applications., which makes it also a promising suggestion for infection-proof biomaterial development.

Brevinin-2GHk from Sylvirana guentheri and the Design of Truncated Analogs Exhibiting the Enhancement of Antimicrobial Activity

Brevinins are an important antimicrobial peptide (AMP) family discovered in the skin secretions of Ranidae frogs. The members demonstrate a typical C-terminal ranabox, as well as a diverse range of other structural characteristics. In this study, we identified a novel brevinin-2 peptide from the skin secretion of Sylvirana guentheri, via cloning transcripts, and identifying the expressed mature peptide, in the skin secretion. The confirmed amino acid sequence of the mature peptide was designated brevinin-2GHk (BR2GK). Moreover, as a previous study had demonstrated that the N-terminus of brevinin-2 is responsible for exerting antimicrobial activity, we also designed a series of truncated derivatives of BR2GK. The results show that the truncated derivatives exhibit significantly improved antimicrobial activity and cytotoxicity compared to the parent peptide, except a Pro¹⁴ substituted analog. The circular dichroism (CD) analysis of this analog revealed that it did not fold into a helical conformation in the presence of either lipopolysaccharides (LPS) or TFE, indicating that position 14 is involved in the formation of the α-helix. Furthermore, three more analogs with the substitutions of Ala, Lys and Arg at the position 14, respectively, revealed the influence on the membrane disruption potency on bacteria and mammalian cells by the structural changes at this position. Overall, the N-terminal 25-mer truncates demonstrated the potent antimicrobial activity with low cytotoxicity.

Bv8-Like Toxin from the Frog Venom of Amolops jingdongensis Promotes Wound Healing via the Interleukin-1 Signaling Pathway

Prokineticins are highly conserved small peptides family expressed in all vertebrates, which contain a wide spectrum of functions. In this study, a prokineticin homolog (Bv8-AJ) isolated from the venom of frog Amolops jingdongensis was fully characterized. Bv8-AJ accelerated full-thickness wounds healing of mice model by promoting the initiation and the termination of inflammatory phase. Moreover, Bv8-AJ exerted strong proliferative effect on fibroblasts and keratinocytes isolated from newborn mice by activating interleukin (IL)-1 production. Our findings indicate that Bv8 is a potent wound healing regulator and may reveal the mechanism of rapid wound-healing in amphibian skins.

Bioevaluation of Ranatuerin-2Pb from the Frog Skin Secretion of Rana pipiens and its Truncated Analogues

Antimicrobial peptides (AMPs) are considered as a promising agent to overcome the drug-resistance of bacteria. Large numbers of AMPs have been identified from the skin secretion of Rana pipiens, including brevinins, ranatuerins, temporins and esculentins. In this study, the cDNA precursor of a broad-spectrum antimicrobial peptide, ranatuerin-2Pb, was cloned and identified. Additionally, two truncated analogues, RPa and RPb, were synthesised to investigate the structure-activity relationship of ranatuerin-2Pb. RPa lost antimicrobial activity against Candida albicans, MRSA, Enterococcus faecalis and Pseudomonas aeruginosa, while RPb retained its broad-spectrum antimicrobial activity. Additionally, ranatuerin-2Pb, RPa and RPb demonstrated inhibition and eradication effects against Staphylococcus aureus biofilm. RPb showed a rapid bacterial killing manner via membrane permeabilization without damaging the cell membrane of erythrocytes. Moreover, RPb decreased the mortality of S. aureus infected Galleria mellonella larvae. Collectively, our results suggested that RPb may pave a novel way for natural antimicrobial drug design.

LFB: A Novel Antimicrobial Brevinin-Like Peptide from the Skin Secretion of the Fujian Large Headed Frog, Limnonectes fujianensi

Amphibians are a natural source of abundant antimicrobial peptides and thus have been widely investigated for isolation of such biomolecules. Many new antimicrobial peptide families have been discovered from amphibians. In this study, a novel antimicrobial peptide named Limnonectes fujianensis Brevinvin (LFB) has been identified in the skin secretion from the Fujian large headed frog, Limnonectes fujianensis. The cDNA sequence was cloned from a skin secretion library and the predicted mature peptide was identified through MS/MS fragmentation sequencing of reverse phase HPLC fractions on the same sample. LFB was predicted to be an amphipathic, hydrophobic, alpha helical, and beta turn peptide that inserts into a lipid bilayer in order to kill the cells. In antimicrobial assays, a synthetic replicate of this novel antimicrobial peptide demonstrated significant activity against the Gram-positive bacterium Staphylococcus aureus, the Gram-negative bacterium Escherichia coli and the yeast, Candida albicans. This novel peptide was highly potent (MIC 4.88 uM) against Gram-negative bacterium, and also has the ability to inhibit the growth of human cancer cell lines with IC₅₀ values ranging from 18.9 μM down to 2.0 μM. These findings help to enrich our understanding of Brevinin-like peptides. Moreover, the data presented here validate frog secretion as a source of potential novel antimicrobial peptides, that also exhibit anti-tumor properties, that could be useful for the treatment of cancer.