Effect of Secondary Structure and Side Chain Length of Hydrophobic Amino Acid Residues on the Antimicrobial Activity and Toxicity of 14‐Residue‐Long de novo AMPs

Abstract

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.

Effect of monovalent salt concentration and peptide secondary structure in peptide-micelle binding

“…Thus, the concentration of peptide in MD was much larger than the MIC against several ESKAPE pathogens (1–10 M) and in CD experiments (100 μM). 41 High concentration of peptide resulted in faster binding of peptide to micelle (within 5 ns for various MD models). Using a larger water-box could be an alternative for lowering the peptide concentration, but would incur huge computational cost, rendering it impractical.…”

“…[38][39][40] In our present study, we have tried to understand the reason for the salt sensitivity of a synthetic AMP, LL-14 that was earlier reported by our group. 41 Cationic fourteen residue long membranolytic LL-14 (Fig. 1), was shown to have high activity (MIC99 $1-10 mM) against several strains of ESKAPE pathogens and fungal strains.…”

“…1 ), was shown to have high activity (MIC99 ∼1–10 μM) against several strains of ESKAPE pathogens and fungal strains. 41 However, the activity of LL-14 was salt-sensitive against several microbes ( P. aeruginosa , S. aureus , C. neoformans ) leading to a partial loss of activity at physiological NaCl concentrations.…”

Is It Possible to Create Antimicrobial Peptides Based on the Amyloidogenic Sequence of Ribosomal S1 Protein of P. aeruginosa?

“…Thus, according to the predictions of the JPred4 and PredictProtein programs, the replacement of the glycine residue with sarcosine in the linker region of the peptide ("CPP"+"linker GGGG"+"predicted amyloidogenic-fragment") affects the results of predicting the secondary structure of the peptide in its amyloidogenic region. In turn, a change in the secondary structure, can lead to a change in the antimicrobial action of peptides [69].…”

Antimicrobial Peptides and Proteins: From Nature’s Reservoir to the Laboratory and Beyond

“…Long hydrophobic side chain in Leu led to the best activity and highest cytotoxicity in LL-14 of all the three peptides. VV-14 was optimally active and non-cytotoxic (Pandit et al, 2021) (Figure 6A). While LL-14 and VV-14 formed α-helices in presence of membrane mimics, ββ-14 remained unstructured.…”