Peptide-based supramolecular assemblies are a promising class of nanomaterials with important biomedical applications, specifically in drug delivery and tissue regeneration. However, the intrinsic antibacterial capabilities of these assemblies have been largely overlooked. The recent identification of common characteristics shared by antibacterial and self-assembling peptides provides a paradigm shift towards development of antibacterial agents. Here we present the antibacterial activity of self-assembled diphenylalanine, which emerges as the minimal model for antibacterial supramolecular polymers. The diphenylalanine nano-assemblies completely inhibit bacterial growth, trigger upregulation of stress-response regulons, induce substantial disruption to bacterial morphology, and cause membrane permeation and depolarization. We demonstrate the specificity of these membrane interactions and the development of antibacterial materials by integration of the peptide assemblies into tissue scaffolds. This study provides important insights into the significance of the interplay between self-assembly and antimicrobial activity and establishes innovative design principles toward the development of antimicrobial agents and materials.

The phenomenon of protein aggregation into amyloid fibrils is associated with a large number of major diseases of unrelated etiology. Unraveling the mechanism of amyloid self-assembly and identifying therapeutic directions to control this process are of utmost importance. Research in this field has been hampered by several challenges, including reproducibility, low protein purification yields, and the inherent aggregation propensity of amyloidogenic proteins, making them extremely difficult to study. Herein, on the basis of the similarity in the assembly mechanism, as well as the physical, chemical, and biological characteristics, of diphenylalanine nanostructures and aromatic amino acid containing amyloid fibrils, we report a simple, yet robust peptide-based platform that could be used for screening of small molecules potentially capable of interfering with the aggregation process and for mechanistic exploration of their mode of action. The system was validated using four small-molecule inhibitors, and the effect was examined via turbidity assay, thioflavin T fluorescence, and electron microscopy. The aggregation profile of diphenylalanine was very similar to that of β-amyloid polypeptide in the presence of the modulators. Rosmarinic acid emerged as an extremely potent inhibitor and a destabilizer of the aggregates. The effect of stoichiometric variation of rosmarinic acid on the process of destabilization was also probed using a microfluidic technique. Finally, the formation of equimolar complexes of diphenylalanine and inhibitors was detected using mass spectrometry. This approach not only provides a system for high-throughput screening of possible inhibitor molecules from larger libraries of modulators, but is also highly useful for understanding the mechanistic aspects of the interactions leading to the process of inhibition.

Fibrillar deposits formed by the aggregation of the human islet amyloid polypeptide (hIAPP) are the major pathological hallmark of type 2 diabetes mellitus (T2DM). Inhibiting the aggregation of hIAPP is considered the primary therapeutic strategy for the treatment of T2DM. Hydroxylated carbon nanoparticles have received great attention in impeding amyloid protein fibrillation owing to their reduced cytotoxicity compared to the pristine ones. In this study, we investigated the influence of hydroxylated single-walled carbon nanotubes (SWCNT-OHs) on the first step of hIAPP aggregation: dimerization by performing explicit solvent replica exchange molecular dynamics (REMD) simulations. Extensive REMD simulations demonstrate that SWCNT-OHs can dramatically inhibit interpeptide β-sheet formation and completely suppress the previously reported β-hairpin amyloidogenic precursor of hIAPP. On the basis of our simulation results, we proposed that SWCNT-OH can hinder hIAPP fibrillation. This was further confirmed by our systematic turbidity measurements, thioflavin T fluorescence, circular dichroism (CD), transmission electron microscope (TEM), and atomic force microscopy (AFM) experiments. Detailed analyses of hIAPP-SWCNT-OH interactions reveal that hydrogen bonding, van der Waals, and π-stacking interactions between hIAPP and SWCNT-OH significantly weaken the inter- and intrapeptide interactions that are crucial for β-sheet formation. Our collective computational and experimental data reveal not only the inhibitory effect but also the inhibitory mechanism of SWCNT-OH against hIAPP aggregation, thus providing new clues for the development of future drug candidates against T2DM.

Designed to deliver: Carbon nanotube (CNT)/amphiphile hybrids with remarkable stability and cell viability under biologically relevant conditions can be obtained by rational modification of the molecular structure of amphiphilic dispersing agents (see scheme; PEG= poly(ethylene glycol)). The CNT/amphiphile hybrids are dispersible in water and efficiently shuttle proteins across mammalian cell membranes.

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