Modification and Targeted Design of N-Terminal Truncates Derived from Brevinin with Improved Therapeutic Efficacy

Development of a novel hybrid antimicrobial peptide for enhancing antimicrobial spectrum and potency against food-borne pathogens

AIMS

To address the increasingly serious challenge of the transmission of foodbrone pathogens in the food chain.

METHODS AND RESULTS

In this study, we employed rational design strategies, including truncation, amino acid substitution, and heterozygosity, to generate seven engineered peptides with α-helical structure, cationic property, and amphipathic characteristics based on the original Abhisin template. Among them, as the hybird antimicrobial peptide (AMP), AM exhibits exceptional stability, minimal toxicity, as well as broad-spectrum and potent antimicrobial activity against foodborne pathogens. Besides, it was observed that the electrostatic incorporation demonstrates by AM results in its primary targeting and disruption of the cell wall and membrane of Escherichia coli O157: H7 (EHEC) and methicillin-resistant Staphylococcus aureus (MRSA), resulting in membrane perforation and enhanced permeability. Additionally, AM effectively counteracts the deleterious effects of lipopolysaccharide, eradicating biofilms and ultimately inducing the demise of both food spoilage and pathogenic microorganisms.

CONCLUSIONS

The findings highlight the significant potential of AM as a highly promising candidate for a novel food preservative and its great importance in the design and optimization of AMP-related agents.

Rational Design and Antimicrobial Potency Assessment of Abaecin Analogues

The widespread and escalating emergence of multidrug resistance is now recognized as one of the most severe global threats to human health. To address the urgent issue of drug-resistant bacteria and the limitation of effective clinical treatments, antimicrobial peptides (AMPs) have been developed as promising substituents of conventional antibiotics. In this study, rational design strategies were employed to acquire seven cationic and α-helical engineered peptides based on the original template of Abaecin. After investigation, we found that AC7 (LLRRWKKLFKKIIRWPRPLPNPGH) demonstrated potent and broad-spectrum antimicrobial activity. Additionally, it demonstrated low cytotoxicity and hemolysis while maintaining good stability. Notably, AC7 displays the antibacterial mechanism with superior abilities in cell membrane disruption and potential DNA binding in vitro, as well as effectively disrupting biofilms. Moreover, the murine skin wound model infected with drug-resistant Pseudomonas aeruginosa was employed to evaluate the anti-infective efficacy and therapeutic potential of AC7. It was observed that AC7 displays a remarkable capacity to inhibit wound colonization, reduce levels of inflammatory cytokines (TNF-α) and inflammatory cells (white blood cells (WBC), monocytes (MONO), lymphocytes (LYMPH), neutrophils (GRAN)), promote the levels of IL-10 and VEGF, and enhance wound healing. Overall, these findings demonstrate the potential of AC7 as a viable alternative to traditional antibiotics.

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.

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.

In Vitro & In Vivo Studies on Identifying and Designing Temporin-1CEh from the Skin Secretion of Rana chensinensis as the Optimised Antibacterial Prototype Drug

Amphibian skin secretion is an ideal source of antimicrobial peptides that are difficult to induce drug resistance to due to their membrane-targeting mechanism as a new treatment scheme. In this study, a natural antimicrobial peptide Temporin-1CEh was identified by molecular cloning and mass spectrometry from the skin secretions of the Chinese forest frog (Rana chensinensis). Through the study of the structure and biological activity, it was found that Temporin-1CEh was a helical peptide from the Temporin family, and possessed good anti-Gram-positive bacteria activity through the mechanism of membrane destruction. Seven analogues were further designed to obtain broad-spectrum antimicrobial activity and higher stability in different physiological conditions. The results showed that T1CEh-KKPWW showed potent antibacterial activity with significantly increasing the activity against Gram-negative bacteria in vitro and in vivo with low haemolysis. In addition, T1CEh-KKPWW2 showed high sensitivity to the pH, serum or salts conditions, which applied a branched structure to allow the active units of the peptide to accumulate. Even though the haemolytic activity was increased, the stable antibacterial activity made this novel analogue meet the conditions to become a potential candidate in future antimicrobial and antibiofilm applications.

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.

Modification Strategy of D-leucine Residue Addition on a Novel Peptide from Odorrana schmackeri, with Enhanced Bioactivity and In Vivo Efficacy

Brevinins are a well-characterised, frog-skin-derived, antimicrobial peptide (AMP) family, but their applications are limited by high cytotoxicity. In this study, a wild-type des-Leu2 brevinin peptide, named brevinin-1OS (B1OS), was identified from Odorrana schmackeri. To explore the significant role of the leucine residue at the second position, two variants, B1OS-L and B1OS-D-L, were designed by adding L-leucine and D-leucine residues at this site, respectively. The antibacterial and anticancer activities of B1OS-L and B1OS-D-L were around ten times stronger than the parent peptide. The activity of B1OS against the growth of Gram-positive bacteria was markedly enhanced after modification. Moreover, the leucine-modified products exerted in vivo therapeutic potential in an methicillin-resistant Staphylococcus aureus (MRSA)-infected waxworm model. Notably, the single substitution of D-leucine significantly increased the killing speed on lung cancer cells, where no viable H838 cells survived after 2 h of treatment with B1OS-D-L at 10 μM with low cytotoxicity on normal cells. Overall, our study suggested that the conserved leucine residue at the second position from the N-terminus is vital for optimising the dual antibacterial and anticancer activities of B1OS and proposed B1OS-D-L as an appealing therapeutic candidate for development.

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