Bacterial Aggregation Triggered by Fibril Forming Tryptophan-Rich Sequences: Effects of Peptide Side Chain and Membrane Phospholipids

Abstract

The influence of side chain residue and phospholipid characteristics of the cytoplasmic membrane upon the fibrillation and bacterial aggregation of arginine (Arg) and tryptophan (Trp) rich antimicrobial peptides (AMPs) has not been well described to date. Here, we utilized the structural advantages of HHC-10 and 4HarHHC-10 (Har, l-homoarginine) that are highly active Trp-rich AMPs and investigated their fibril formation and activity behavior against bacteria. The peptides revealed time-dependent self-assembly of polyproline II (PPII) α-helices, but by comparison, 4HarHHC-10 tended to form higher ordered fibrils due to relatively strong cation−π stacking of Trp with Har residue. Both peptides rapidly killed S. aureus and E. coli at their MICs and caused aggregation of bacteria at higher concentrations. This bacterial aggregation was accompanied by the formation of morphologically distinct electron-dense nanostructures, likely including but not limited to peptides alone. Both HHC-10-derived peptides caused blebs and buds in the E. coli membrane that are rich in POPE phospholipid that promotes negative curvature. However, the main population of S. aureus cells retained their cocci structure upon treatment with HHC peptides even at concentration higher than the MICs. In contrast, the cell aggregation was not induced by HHC fibrils that were most likely stabilized through intra-/intermolecular cation−π stacking. It is proposed that masking of these interactions might have resulted in diminished membrane association/insertion of the HHC nanostructures. The peptides caused aggregation of POPC/POPG (1/3) and POPE/POPG (3/1) liposomes. Nonetheless, disaggregation of the former vesicles was observed at ratios of lipid to peptide of greater than 6 and 24 for HHC-10 and 4HarHHC-10, respectively. Collectively, our results revealed dose-dependent bacterial aggregation mediated by Trp-rich AMPs that was profoundly influenced by the degree of peptide’s self-association and the composition and intrinsic curvature of the cytoplasmic membrane lipids.

Palmitoylation of Membrane-Penetrating Magainin Derivatives Reinforces Necroptosis in A549 Cells Dependent on Peptide Conformational Propensities

“…The A549 cells were incubated in the 6-well microplates at the concentration of ∼5.0 × 10 5 for 24 h ( T = 37 °C), treated with P1MK5E at IC 50 for 2 h, followed by immediate discarding of the supernatant and PBS-washing, and prepared for the electron imaging according to our slightly modified protocols …”

IAMPE: NMR-Assisted Computational Prediction of Antimicrobial Peptides

“…The AMPs are a class of bioactive molecules present in the immune system of many organisms that are potentially supposed to be the next generation of antibiotics against resistant pathogens. − Although peptides of different lengths and amino acid compositions have been discovered so far, the AMPs’ sequences need to be optimized with respect to their natural properties against the growing concerns of ineffective current antibiotics. In contrast to the costly and time-consuming laboratory-based techniques, several machine learning tools have already been developed for the evaluation, prediction, and design of novel AMPs.…”

“…The AMPs are considered as a primitive class of defense mechanisms in a variety of eukaryotic and prokaryotic organisms. , A plethora of these gene-encoded peptides is immediately mobilized followed by the microbial infections. The AMPs have common properties, including the molecular mass of about 0.3–5 kDa, overall net positive charge, hydrophobic nature, and membrane-lytic mode of action. , These sequences may be categorized in terms of their lengths, primary structures (their distinctive amino acid composite), and the presence or absence of disulfide bridges . Despite these effects, the AMPs suffer inherent drawbacks, such as patent monopoly for economic concerns, high costs for synthesis and bioscreening, limited activity due to the salt, serum, and pH sensitivity, proteolytic stability, unknown systemic and local toxicities, and allergic reactions. , Nevertheless, the design and development of new synthetic AMPs through the manipulation of the peptide structure is an efficient strategy aiming to prevent and treat systemic and topical infections caused by the bacterial superbugs …”

“…The AMPs have common properties, including the molecular mass of about 0.3−5 kDa, overall net positive charge, hydrophobic nature, and membrane-lytic mode of action. 3,4 These sequences may be categorized in terms of their lengths, primary structures (their distinctive amino acid composite), and the presence or absence of disulfide bridges. 2 Despite these effects, the AMPs suffer inherent drawbacks, such as patent monopoly for economic concerns, 5 high costs for synthesis and bioscreening, 5 limited activity due to the salt, serum, and pH sensitivity, 6 proteolytic stability, 7 unknown systemic and local toxicities, and allergic reactions.…”

De Novo Design of Triblock Amphiphilic Short Antimicrobial Peptides

“…At present, designing new AMPs is a highly important issue for scientists. Several research groups have designed diverse mimetic AMPs. − Most researchers assume that mimetic peptides should contain α-helix or β-sheet structures, similar to specific high-activity AMPs; their results supported their hypothesis. − However, natural antibacterial peptides randomly occur, and their antibacterial mechanism has not been well explained. Besides, natural or synthetic antibacterial peptides, which present high activity, usually contain 20–50 amino acids and feature low but expensive synthesis efficiency.…”