Thinking on the Construction of Antimicrobial Peptide Databases: Powerful Tools for the Molecular Design and Screening

The effect of C-terminal deamidation on bacterial susceptibility and resistance to modelin-5

The C-terminal amide carried by antimicrobial peptides (AMPs) can play a variable role in their antibacterial action and here, this role is investigated here for the synthetic peptide modelin-5 (M5-NH2). The peptide showed potent activity against Pseudomonas aeruginosa (MLC = 5.9 µM), with strong binding to the cytoplasmic membrane (CM) (Kd = 21.5 μM) and the adoption of high levels of amphiphilic α-helical structure (80.1%) which promoted strong CM penetration (9.6 mN m-1) and CM lysis (89.0%). In contrast, Staphylococcus aureus was resistant to M5-NH2 (MLC = 139.6 µM), probably due electrostatic repulsion effects mediated by Lys-PG in the organism's CM. These effects promoted weak CM binding (Kd = 120.6 μM) and the formation of low levels of amphiphilic α-helical structure (30.1%), with low levels of CM penetration (4.8 mN m-1) and lysis (36.4%). C-terminal deamidation had a variable influence on the antibacterial activity of M5-NH2, and in the case of S. aureus, loss of this structural moiety had no apparent effect on activity. The resistance of S. aureus to M5-NH2 isoforms appeared to be facilitated by the high level of charge carried by these peptides, as well as the density and distribution of this charge. In the case of P. aeruginosa, the activity of M5-NH2 was greatly reduced by C-terminal deamidation (MLC = 138.6 µM), primarily through decreased CM binding (Kd = 118.4 μM) and amphiphilic α-helix formation (39.6%) that led to lower levels of CM penetration (5.1 mN m-1) and lysis (39.0%).

Advances in Artificially Designed Antibacterial Active Antimicrobial Peptides

Antibacterial resistance has emerged as a significant global concern, necessitating the urgent development of new antibacterial drugs. Antimicrobial peptides (AMPs) are naturally occurring peptides found in various organisms. Coupled with a wide range of antibacterial activity, AMPs are less likely to develop drug resistance and can act as potential agents for treating bacterial infections. However, their characteristics, such as low activity, instability, and toxicity, hinder their clinical application. Consequently, researchers are inclined towards artificial design and optimization based on natural AMPs. This review discusses the research advancements in the field of artificial designing and optimization of various AMPs. Moreover, it highlights various strategies for designing such peptides, aiming to provide valuable insights for developing novel AMPs.

An amphipathic peptide combats multidrug-resistant Staphylococcus aureus and biofilms

The emergence of drug-resistant Staphylococcus aureus (S. aureus) has resulted in infections in humans and animals that may lead to a crisis in the absence of highly effective drugs. Consequently, the development of alternative or complementary antimicrobial agents is urgently needed. Here, a series of peptides derived from AP138 were designed with high expression, antimicrobial activity, and antibiofilm properties via bioinformatics. Among them, the best derived peptide, A24 (S9A), demonstrated the greatest stability and bactericidal efficiency against multidrug-resistant S. aureus in a physiological environment, with a high hydrophobicity of 35%. This peptide exhibited superior performance compared to the preclinical or clinical antimicrobial peptides (AMPs). A24 displayed increased biocompatibility in vitro and in vivo, exhibiting a low hemolysis rate (less than 3%), minimal cytotoxicity (survival rate exceeding 85%), and no histotoxicity. A24 had the capacity to destroy cell walls, increase cell membrane permeability, and induce increases in intracellular ATP and ROS levels, which resulted in the rapid death of S. aureus. A24 inhibited the formation of early biofilms and eliminated both mature biofilms (40-50%) and persisters (99.9%). Therapeutic doses of A24 were shown to exhibit favorable safety profiles and bactericidal efficacy in vivo and could reduce bacterial loads of multidrug-resistant S. aureus by 4-5 log10 CFU/0.1g levels in mouse peritonitis and endometritis models. Furthermore, A24 increased the survival rate to 100% and exhibited anti-inflammatory properties in a mouse model. The aforementioned data illustrate the potential of A24 as a pharmaceutical agent for the treatment of bacterial infections, including peritonitis and endometritis, in animal husbandry with multidrug-resistant S. aureus infections.

Development strategies and application of antimicrobial peptides as future alternatives to in-feed antibiotics

The use of in-feed antibiotics has been widely restricted due to the significant environmental pollution and food safety concerns they have caused. Antimicrobial peptides (AMPs) have attracted widespread attention as potential future alternatives to in-feed antibiotics owing to their demonstrated antimicrobial activity and environment friendly characteristics. However, the challenges of weak bioactivity, immature stability, and low production yields of natural AMPs impede practical application in the feed industry. To address these problems, efforts have been made to develop strategies for approaching the AMPs with enhanced properties. Herein, we summarize approaches to improving the properties of AMPs as potential alternatives to in-feed antibiotics, mainly including optimization of structural parameters, sequence modification, selection of microbial hosts, fusion expression, and industrially fermentation control. Additionally, the potential for application of AMPs in animal husbandry is discussed. This comprehensive review lays a strong theoretical foundation for the development of in-feed AMPs to achieve the public health globally.

Effect of Camel Peptide on the Biofilm of Staphylococcus epidermidis and Staphylococcus haemolyticus Formed on Orthopedic Implants

The increasing bacterial drug resistance and the associated challenges in the treatment of infections warrant the search for alternative therapeutic methods. Hope is placed in antimicrobial peptides, which have a broad spectrum of action and are effective against strains which are resistant to conventional antibiotics. Antimicrobial peptides are also tested for their efficacy in the treatment of infections associated with the formation of biofilm. The aim of the present study was to examine the effect of Camel peptide on S. epidermidis and S. haemolyticus adhesion to and formation of biofilm on steel cortical bone screws and also on the process of reducing mature biofilm in orthopedic implants. The tests were performed on steel implants for osteosynthesis. The MIC value and MBEC values of the peptide were determined using the microdilution method in microtiter plates. The effect of the peptide on adhesion and biofilm formation, as well as on the activity on the preformed biofilm, was evaluated using quantitative methods and confocal microscopy. The presented research results indicate that the peptide exhibits very good antimicrobial properties against the analyzed strains. Concentrations above MIC reduced biofilm in the range of 90-99%.

Site Mutation Improves the Expression and Antimicrobial Properties of Fungal Defense

Although antimicrobial peptides (AMPs) have highly desirable intrinsic characteristics in their commercial product development as new antimicrobials, the limitations of AMPs from experimental to scale development include the low oral bioavailability, and high production costs due to inadequate in vitro/in vivo gene expression- and low scale. Plectasin has good bactericidal activity against Staphylococcus and Streptococcus, and the selective bactericidal activity greatly reduces the damage to the micro-ecosystem when applied in vivo. However, its expression level was relatively low (748.63 mg/L). In view of these situations, this study will optimize and modify the structure of Plectasin, hoping to obtain candidates with high expression, no/low toxicity, and maintain desirable antibacterial activity. Through sequence alignment, Plectasin was used as a template to introduce the degenerate bases, and the screening library was constructed. After three different levels of screening, the candidate sequence PN7 was obtained, and its total protein yield in the supernatant was 5.53 g/L, with the highest value so far for the variants or constructs from the same ancestor source. PN7 had strong activity against several species of Gram-positive bacteria (MIC value range 1~16 μg/mL). It was relatively stable in various conditions in vitro; in addition, the peptide showed no toxicity to mice for 1 week after intraperitoneal injection. Meanwhile, PN7 kills Staphylococcus aureus ATCC 43300 with a mode of a quicker (>99% S. aureus was killed within 2 h, whereas vancomycin at 2× MIC was 8 h.) and longer PAE period. The findings indicate that PN7 may be a novel promising antimicrobial agent, and this study also provides a model or an example for the design, modification, or reconstruction of novel AMPs and their derivatives.

Progress towards the clinical use of antimicrobial peptides: challenges and opportunities

INTRODUCTION

To overcome the challenge of multidrug resistance, natural and synthetic peptides are candidates to become the basis of innovative therapeutics, featuring diverse mechanisms of action. Traditionally, the time elapsed from medical discoveries to their application is long. The urgency derived from the emergence of antibiotic resistance recommends an acceleration of research to put the new weapons in the hands of clinicians.

AREAS COVERED

This narrative review introduces ideas and suggestions of new strategies that may be used as a basis upon which to recommend reduced development times and to facilitate the arrival of new molecules in the fight against microbes.

EXPERT OPINION

Although studies on new innovative antimicrobial treatments are being conducted, sooner rather than later, more clinical trials, preclinical and translational research are needed to promote the development of innovative antimicrobial treatments for multidrug resistant infections. The situation is worrying, no less than that generated by pandemics such as the ones we have just experienced and conflicts such as world wars. Although from the point of view of human perception, resistance to antibiotics may not seem as serious as these other situations, it is possibly the hidden pandemic that most jeopardizes the future of medicine.

Molecular Modification of Kex2 P1' Site Enhances Expression and Druggability of Fungal Defensin

Pichia pastoris is the widely used expression system for producing recombinant secretory proteins. It is known that Kex2 protease plays a vital role in the process of protein secretion, in which the P1' site affects its cleavage efficiency. To enhance the expression level of fungal defensin-derived peptide NZ2114, this work attempts to optimize the P1' site of Kex2 by replacing it with 20 amino acids in turn. The results showed that when the amino acid of the P1' site was changed to Phe (F), the yield of target peptide significantly increased from 2.39 g/L to 4.81 g/L. Additionally, the novel peptide F-NZ2114 (short for FNZ) showed strong antimicrobial activity against Gram-positive (G⁺) bacteria, especially for Staphylococcus aureus and Streptococcus agalactiae (MIC: 4-8 μg/mL). The FNZ was very stable and retained high activity in various conditions; in addition, a low cytotoxicity and no hemolysis were observed even at a high concentration of 128 μg/mL, and a longer postantibiotic effect was reached. The above results indicate that this engineering strategy provided a feasible optimization scheme for enhancing the expression level and druggability of this antimicrobial peptide from fungal defensin and other similar targets by this updated recombinant yeast.