Targeting nucleic acid phase transitions as a mechanism of action for antimicrobial peptides

Metallo-Glycodendrimeric Materials against Enterotoxigenic Escherichia coli

Conjugation of carbohydrates to nanomaterials has been extensively studied and recognized as an alternative in the biomedical field. Dendrimers synthesized with mannose at the end group and with entrapped zero-valent copper/silver could be a potential candidate against bacterial proliferation. This study is aimed at investigating the bactericidal activity of metal-glycodendrimers. The Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction was used to synthesize a new mannosylated dendrimer containing 12 mannopyranoside residues in the periphery. The enterotoxigenic Escherichia coli fimbriae 4 (ETEC:F4) viability, measured at 600 nm, showed the half-inhibitory concentration (IC50) of metal-free glycodendrimers (D), copper-loaded glycodendrimers (D:Cu) and silver-loaded glycodendrimers (D:Ag) closed to 4.5 × 101, 3.5 × 101 and to 1.0 × 10-2 µg/mL, respectively, and minimum inhibitory concentration (MIC) of D, D:Cu and D:Ag of 2.0, 1.5 and 1.0 × 10-4 µg/mL, respectively. The release of bacteria contents onto broth and the inhibition of ETEC:F4 biofilm formation increased with the number of metallo-glycodendrimer materials, with a special interest in silver-containing nanomaterial, which had the highest activity, suggesting that glycodendrimer-based materials interfered with bacteria-bacteria or bacteria-polystyrene interactions, with bacteria metabolism and can disrupt bacteria cell walls. Our findings identify metal-mannose-dendrimers as potent bactericidal agents and emphasize the effect of entrapped zero-valent metal against ETEC:F4.

Recent advances in antimicrobial peptide-based therapy

Antimicrobial peptides (AMPs) are a group of polypeptide chains that have the property to target and kill a myriad of microbial organisms including viruses, bacteria, protists, etc. The first discovered AMP was named gramicidin, an extract of aerobic soil bacteria. Further studies discovered that these peptides are present not only in prokaryotes but in eukaryotes as well. They play a vital role in human innate immunity and wound repair. Consequently, they have maintained a high level of intrigue among scientists in the field of immunology, especially so with the rise of antibiotic-resistant pathogens decreasing the reliability of antibiotics in healthcare. While AMPs have promising potential to substitute for common antibiotics, their use as effective replacements is barred by certain limitations. First, they have the potential to be cytotoxic to human cells. Second, they are unstable in the blood due to action by various proteolytic agents and ions that cause their degradation. This review provides an overview of the mechanism of AMPs, their limitations, and developments in recent years that provide techniques to overcome those limitations. We also discuss the advantages and drawbacks of AMPs as a replacement for antibiotics as compared to other alternatives such as synthetically modified bacteriophages, traditional medicine, and probiotics.

Charge-Patterned Disordered Peptides Tune Intracellular Phase Separation in Bacteria

Subcellular phase-separated compartments, known as biomolecular condensates, play an important role in the spatiotemporal organization of cells. To understand the sequence-determinants of phase separation in bacteria, we engineered protein-based condensates in Escherichia coli using electrostatic interactions as the main driving force. Minimal cationic disordered peptides were used to supercharge negative, neutral, and positive globular model proteins, enabling their phase separation with anionic biomacromolecules in the cell. The phase behavior was governed by the interaction strength between the cationic proteins and anionic biopolymers, in addition to the protein concentration. The interaction strength primarily depended on the overall net charge of the protein, but the distribution of charge between the globular and disordered domains also had an impact. Notably, the protein charge distribution between domains could tune mesoscale attributes such as the size, number, and subcellular localization of condensates within E. coli cells. The length and charge density of the disordered peptides had significant effects on protein expression levels, ultimately influencing the formation of condensates. Taken together, charge-patterned disordered peptides provide a platform for understanding the molecular grammar underlying phase separation in bacteria.