Herein we report the efficacy and toxicity of three de novo designed cationic antimicrobial peptides (AMPs) LL‐14, VV‐14 and ββ‐14, where side chains of the hydrophobic amino acids were reduced gradually. The AMPs showed broad‐spectrum antimicrobial activity against three pathogens from the ESKAPE group and two fungal strains. This study showed that side chains which are either too long or too short increase toxicity and lower antimicrobial activity, respectively. VV‐14 was found to be non‐cytotoxic and highly potent under physiological salt concentrations against several pathogens, especially Salmonella typhi TY2. These AMPs acted via membrane deformation, depolarization, and lysis. The activity of the AMPs is related to their ability to take on amphipathic helical conformations in the presence of microbial membrane mimics. Among AMPs with the same charge, hydrophobic interactions between the side chains of the residues with cell membrane lipids determine their antimicrobial potency and cytotoxicity. Strikingly, an optimum hydrophobic interaction is the crux of generating highly potent non‐cytotoxic AMPs.

Antimicrobial peptides have gained widespread attention as an alternative to the conventional antibiotics for combating microbial infections. Here, we report a detailed structure-function correlation of two nontoxic, nonhemolytic, and salt-tolerant de novo designed seven-residue leucine-lysine-based peptides, NHLKWLKKLCONH (P4) and NHLRWLRRLCONH (P5), with strong antimicrobial and antifungal activity. Biological experiments, low- and high-resolution spectroscopic techniques in conjunction with molecular dynamics simulation studies, could establish the structure-function correlation. The peptides are unstructured both in water and in bacterial membrane mimicking environment, suggesting that the secondary structure does not play a major role in their activity. Our studies could justify the probable membranolytic mode of action for killing the pathogens. Attempts to understand the mode of action of these small AMPs is fundamental in the rational design of more potential therapeutic molecules beyond serendipity in the future.

Pseudomonas aeruginosa is an opportunistic bacterial pathogen causing severe infections in hospitalized and immunosuppressed patients, particularly individuals affected by cystic fibrosis. Several clinically isolated P. aeruginosa strains were found to be resistant to three or more antimicrobial classes indicating the importance of identifying new antimicrobials active against this pathogen. Here, we characterized the antimicrobial activity and the action mechanisms against P. aeruginosa of two natural isoforms of the antimicrobial peptide cecropin B, both isolated from the silkworm Bombyx mori. These cecropin B isoforms differ in a single amino acid substitution within the active portion of the peptide, so that the glutamic acid of the E53 CecB variant is replaced by a glutamine in the Q53 CecB isoform. Both peptides showed a high antimicrobial and membranolytic activity against P. aeruginosa, with Q53 CecB displaying greater activity compared with the E53 CecB isoform. Biophysical analyses, live-cell NMR, and molecular-dynamic-simulation studies indicated that both peptides might act as membrane-interacting elements, which can disrupt outer-membrane organization, facilitating their translocation toward the inner membrane of the bacterial cell. Our data also suggest that the amino acid variation of the Q53 CecB isoform represents a critical factor in stabilizing the hydrophobic segment that interacts with the bacterial membrane, determining the highest antimicrobial activity of the whole peptide. Its high stability to pH and temperature variations, tolerance to high salt concentrations, and low toxicity against human cells make Q53 CecB a promising candidate in the development of CecB-derived compounds against P. aeruginosa.

No abstract

Alzheimer’s disease (AD) is a severe neurodegenerative disorder caused by abnormal accumulation of toxic amyloid plaques of the amyloid-beta (Aβ) or the tau proteins in the brain. The plaque deposition leading to the collapse of the cellular integrity is responsible for a myriad of surface phenomena acting at the neuronal lipid interface. Recent years have witnessed dysfunction of the blood–brain barriers (BBB) associated with AD. Several studies support the idea that BBB acts as a platform for the formation of misfolded Aβ peptide, promoting oligomerization and fibrillation, compromising the overall integrity of the central nervous system. While the amyloid plaque deposition has been known to be responsible for the collapse of the BBB membrane integrity, the causal effect relationship between BBB and Aβ amyloidogenesis remains unclear. In this study, we have used physiologically relevant synthetic model membrane systems to gain atomic insight into the functional aspects of the lipid interface. Here, we have used a minimalist BBB mimic, POPC/POPG/cholesterol/GM1, to compare with the native BBB (total lipid brain extract (TLBE)), to understand the molecular events occurring in the membrane-induced Aβ40 amyloid aggregation. Our study showed that the two membrane models accelerated the Aβ40 aggregation kinetics with differential secondary structural transitions of the peptide. The observed structural transitions are defined by the lipid compositions, which in turn undermines the differences in lipid surface phenomena, leading to peptide induced cellular toxicity in the neuronal membrane.