A Designed Analog of an Antimicrobial Peptide, Crabrolin, Exhibits Enhanced Anti-Proliferative and In Vivo Antimicrobial Activity

Antimicrobial peptides have gradually attracted interest as promising alternatives to conventional agents to control the worldwide health threats posed by antibiotic resistance and cancer. Crabrolin is a tridecapeptide extracted from the venom of the European hornet (Vespa crabro). Its antibacterial and anticancer potentials have been underrated compared to other peptides discovered from natural resources. Herein, a series of analogs were designed based on the template sequence of crabrolin to study its structure-activity relationship and enhance the drug's potential by changing the number, type, and distribution of charged residues. The cationicity-enhanced derivatives were shown to have improved antibacterial and anticancer activities with a lower toxicity. Notably, the double-arginine-modified product, crabrolin-TR, possessed a potent capacity against Pseudomonas aeruginosa (minimum inhibitory concentration (MIC) = 4 μM), which was around thirty times stronger than the parent peptide (MIC = 128 μM). Furthermore, crabrolin-TR showed an in vivo treatment efficacy in a Klebsiella-pneumoniae-infected waxworm model and was non-toxic under its maximum MBC value (MIC = 8 μM), indicating its therapeutic potency and better selectivity. Overall, we rationally designed functional peptides by progressively increasing the number and distribution of charged residues, demonstrating new insights for developing therapeutic molecules from natural resources with enhanced properties, and proposed crabrolin-TR as an appealing antibacterial and anticancer agent candidate for development.

Structural and Functional Characterization of the Newly Designed Antimicrobial Peptide Crabrolin21

(1) Background: antimicrobial resistance is becoming a dramatic problem for public health, and the design of new antimicrobial agents is an active research area. (2) Methods: based on our previous work, we designed an improved version of the crabrolin peptide and characterized its functional and structural properties with a wide range of techniques. (3) Results: the newly designed peptide, crabrolin21, is much more active than the previous ones and shows specific selectivity towards bacterial cells. (4) Conclusions: crabrolin21 shows interesting properties and deserves further studies.

Unraveling the Role of Antimicrobial Peptides in Insects

Antimicrobial peptides (AMPs) are short, mainly positively charged, amphipathic molecules. AMPs are important effectors of the immune response in insects with a broad spectrum of antibacterial, antifungal, and antiparasitic activity. In addition to these well-known roles, AMPs exhibit many other, often unobvious, functions in the host. They support insects in the elimination of viral infections. AMPs participate in the regulation of brain-controlled processes, e.g., sleep and non-associative learning. By influencing neuronal health, communication, and activity, they can affect the functioning of the insect nervous system. Expansion of the AMP repertoire and loss of their specificity is connected with the aging process and lifespan of insects. Moreover, AMPs take part in maintaining gut homeostasis, regulating the number of endosymbionts as well as reducing the number of foreign microbiota. In turn, the presence of AMPs in insect venom prevents the spread of infection in social insects, where the prey may be a source of pathogens.

Generation of truncated derivatives through in silico enzymatic digest of peptide GV30 target MRSA both in vitro and in vivo

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A novel host-defence peptide GV30 was identified from the frog skin secretion of Hylarana guentheri.

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Seven short AMPs were generated by in silico enzymatic digest of GV30 using an online proteomic bioinformatic tool PeptideCutter in ExPASy server.

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Two truncated products, GV23 and GV21, exhibited an improved antibacterial effect against MRSA in vitro and demonstrated a faster bactericidal effect than the parent peptide.

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GV 21 was found to have a better in vivo anti-MRSA activity and retain the good antibacterial activity under salt and serum conditions, along with lower toxicity.

Methicillin-resistant Staphylococcus aureus (MRSA) causing serious hospital-acquired infections and skin infections has become a “superbug” in clinical treatment. Although the clinical treatment of MRSA is continuously improving, due to its unceasing global spread, MRSA has produced much heated discussion and focused study, therefore suggesting an urgent task to find new antibacterial drugs to combat this issue. Antimicrobial peptides (AMPs) are used as the last-resort drugs for treating multidrug-resistant bacterial infections, but their utilisation is still limited due to their low stability and often strong toxicity.

Here, we evaluated the structure and the bioactivity of an AMP, GV30, derived from the frog skin secretions of Hylarana guentheri, and designed seven truncated derivatives based on the presence of cleavage sites for trypsin using an online proteomic bioinformatic resource PeptideCutter tool. We investigated the anti-MRSA effect, toxicity and salt- and serum-resistance of these peptides. Interestingly, the structure–activity relationship revealed that removing “Rana box” loop could significantly improve the bactericidal speed on MRSA. Among these derivatives, GV21 (GVIFNALKGVAKTVAAQLLKK-NH₂), because of its faster antibacterial effect, lower toxicity, and retains the good antibacterial activity and stability of the parent peptide, is considered to become a new potential antibacterial candidate against MRSA.

Outer membrane and phospholipid composition of the target membrane affect the antimicrobial potential of first- and second-generation lipophosphonoxins

Lipophosphonoxins (LPPOs) are small modular synthetic antibacterial compounds that target the cytoplasmic membrane. First-generation LPPOs (LPPO I) exhibit an antimicrobial activity against Gram-positive bacteria; however they do not exhibit any activity against Gram-negatives. Second-generation LPPOs (LPPO II) also exhibit broadened activity against Gram-negatives. We investigated the reasons behind this different susceptibility of bacteria to the two generations of LPPOs using model membranes and the living model bacteria Bacillus subtilis and Escherichia coli. We show that both generations of LPPOs form oligomeric conductive pores and permeabilize the bacterial membrane of sensitive cells. LPPO activity is not affected by the value of the target membrane potential, and thus they are also active against persister cells. The insensitivity of Gram-negative bacteria to LPPO I is probably caused by the barrier function of the outer membrane with LPS. LPPO I is almost incapable of overcoming the outer membrane in living cells, and the presence of LPS in liposomes substantially reduces their activity. Further, the antimicrobial activity of LPPO is also influenced by the phospholipid composition of the target membrane. A higher proportion of phospholipids with neutral charge such as phosphatidylethanolamine or phosphatidylcholine reduces the LPPO permeabilizing potential.