Self-assembled Peptide Nanostructures Research Articles

Improving the water solubility of cannabidiol using a peptide carrier.

Cannabidiol (CBD), nonpsychotropic cannabinoid found in Cannabis sativa, is a very promising drug candidate offering many differential effects such as sedative, antiinflammatory, antioxidant, and neuroprotective properties. Nevertheless, the therapeutic use of CBD is hindered by its lack of water solubility and relatively low bioavailability. Various carriers have been used to address the solubility issues of CBD and other highly lipophilic drugs so far. However, self-assembled peptide nanostructures as carrier have not been used to improve the water solubility of CBD yet. In this study, a self-assembling peptide micelle was demonstrated to be an effective vehicle for encapsulation of CBD and increased its aqueous solubility up to 2000-fold compared to CBD itself.

Magnetic control of self-assembly and disassembly in organic materials

Because organic molecules and materials are generally insensitive or weakly sensitive to magnetic fields, a certain means to enhance their magnetic responsiveness needs to be exploited. Here we show a strategy to amplify the magnetic responsiveness of self-assembled peptide nanostructures by synergistically combining the concepts of perfect α-helix and rod-coil supramolecular building blocks. Firstly, we develop a monomeric, nonpolar, and perfect α-helix (MNP-helix). Then, we employ the MNP-helix as the rod block of rod-coil amphiphiles (rod-coils) because rod-coils are well-suited for fabricating responsive assemblies. We show that the self-assembly processes of the designed rod-coils and disassembly of rod-coil/DNA complexes can be controlled in a magnetically responsive manner using the relatively weak magnetic field provided by the ordinary neodymium magnet [0.07 ~ 0.25 Tesla (T)]. These results demonstrate that magnetically responsive organic assemblies usable under practical conditions can be realized by using rod-coil supramolecular building blocks containing constructively organized diamagnetic moieties.

Wearable sensors for real-time physiological monitoring based on self-assembled diphenylalanine peptide nanostructures

Self-assembled diphenylalanine short peptides show great potential in wearable and flexible biomedical devices due to its excellent biocompatibility and piezoelectric nature. Herein, the piezoelectric activity of self-assembled diphenylalanine analogues by rationally selecting chemical linkers such as ethylene diamine, succinic acid and terephthalaldehyde. Our results show that the self-assembled diphenylalanine with terepthalaldehyde linker has a favorable effect on the piezoelectric activity. The output of an optimized SP3 PNG can reach 29 V and 480 nA, and, it has exhibited excellent stability, repeatability, and charging-discharging capacity. Such a device can be used to harness energy or detect biomechanical actions such as swallowing, finger bending, coughing, posture angle monitoring and alphabet recognition. The PNG has been used to monitor arterial pulses as a biomedical application model. The obtained results are steppingstones towards developing robust bio-implantable PNGs for powering pacemakers and implantable cardioverter-defibrillators (ICDs) in future.

Steady-state and fluorescence lifetime quenching of self-assembled diphenylalanine/coumarin nanostructures as a method to determine dissolved O2 in water

A fluorescent system formed by the combination of coumarin derivative and self-assembled peptide nanostructures was used as sensing system to determine dissolved oxygen (O2) in water samples. Detection was based on the sensing system fluorescence quenching by O2, measured by steady-state and time-resolved fluorescence spectroscopy and Stern-Volmer plot to correlate fluorescence intensity to O2 concentration in the samples. Also, fluorescence lifetime decays informed about the mechanisms in which the quenching is occurring, indicating that the sensing system is highly sensitive and selective to O2, since quenching occurs by a non-radiative energy transfer from electronic excited singlet states of the system to the O2 molecule. This process was evidenced by the system fluorescence lifetime decrease, yielding Singlet O2 as indicative that this system can also find other technological applications.

Drug delivery with designed peptide hydrogels: Experimental and computational studies.

Self-assembling peptide nanostructures have shown to be of great importance in nature and have many promising applications, for example, in medicine as drug delivery vehicles, biosensors and antivirals. There are numerous interesting candidate molecules within the sequence space built from the 20 amino acids. However, the immense complexity and variety spanned makes it difficult to screen and predict the supramolecular behavior merely based on sequence. Here, we employ a synergistic simulation and experimental approach that can be applied to explore the peptide space and identify peptides for drug delivery applications. These methods cover a broad range of length and time scales, from the very short (i.e., atomic level), via all-atom molecular dynamics (MD) simulations, up to the macroscopic one, via scanning electron microscopy (SEM) experiments. We explore the self-assembly of RAE, RAEF and ALKx (namely ALK1, ALK2 and ALK3) amphipathic peptides in water. The circular dichroism (CD) spectra of peptides illustrates the beta sheet rich superstructures, whereas scanning electron microscopy (SEM) analysis shows the peptide morphology with several hundreds of nanometers of length. The MD simulation provides mechanistic insight into the crucial roles of hydrophilic and hydrophobic amino acids in the assembly of ALKx peptide derivatives; it reveals that assembly capability is reduced by increasing the length of hydrophilic Lys residues in ALKx peptides. Experiments and simulation results are in qualitative agreement. Based on various measures, the strength of the self-assembly propensity of the peptides in aqueous solutions attains the following order: ALK1=ALK2>RAE>ALK3>RAEF. Together this data provides insights into the mechanisms of self-assembly of model peptides. These findings will enable for the bottom-up design of novel peptides, which will serve as the basis for further encapsulation of hydrophobic drugs for drug delivery and tissue engineering applications.

Stimuli-Responsive Membrane Anchor Peptide Nanofoils for Tunable Membrane Association and Lipid Bilayer Fusion.

Self-assembled peptide nanostructures with stimuli-responsive features are promising as functional materials. Despite extensive research efforts, water-soluble supramolecular constructs that can interact with lipid membranes in a controllable way are still challenging to achieve. Here, we have employed a short membrane anchor protein motif (GLFD) and coupled it to a spiropyran photoswitch. Under physiological conditions, these conjugates assemble into ∼3.5 nm thick, foil-like peptide bilayer morphologies. Photoisomerization from the closed spiro (SP) form to the open merocyanine (MC) form of the photoswitch triggers rearrangements within the foils. This results in substantial changes in their membrane-binding properties, which also varies sensitively to lipid composition, ranging from reversible nanofoil reformation to stepwise membrane adsorption. The formed peptide layers in the assembly are also able to attach to various liposomes with different surface charges, enabling the fusion of their lipid bilayers. Here, SP-to-MC conversion can be used both to trigger and to modulate the liposome fusion efficiency.

Structural control of self-assembled peptide nanostructures to develop peptide vesicles for photodynamic therapy of cancer.

Vesicles such as liposomes, polymersomes, and exosomes have been widely used as drug delivery carriers; however, peptide vesicles (peptidesomes) despite their potential utility are far less well developed. Peptidesomes are distinctive because peptides play dual roles as a self-assembly building block and a bioactive functional unit. In order for peptidesomes to become successful nanodrugs, the issues related to differences in nanostructural properties between in vitro and in vivo conditions should be addressed. Here, we delineate a multivariate approach to feedback control the structures of peptide building blocks, nanoparticle size, drug loading process, nanoparticle aggregation, cytotoxicity, cell targeting capability, endosome disruption function, protease resistance, and in vivo performance, which eventually enabled the successful development of a highly efficacious peptidesome for in vivo cancer therapy. This study lays the groundwork for the successful in vivo translation of peptide nanodrugs.

Peptide Coassembly to Enhance Piezoelectricity for Energy Harvesting.

The discovery of piezoelectricity in self-assembled peptide nanostructures opens an avenue to a new regime of piezoelectric materials and enables the fundamental investigation of electromechanical coupling in biomaterials. However, strategies for fabricating peptides with desired properties are still lacking. We find that a peptide-based coassembly process effectively controls the properties of peptide nanomaterials and demonstrates their application potential in nanogenerators. The composing peptides and their concentration influence the morphology, molecular property, and physical property of coassembled crystals. Compared with self-assembled diphenylalanine peptides, the coassembled peptides of diphenylalanine and phenylalanine-tryptophan show a 38% increase in piezoelectric coefficient, and the resulting harvesting device shows nearly a 3-fold increase in open-circuit voltage outputs.

Enzyme-Responsive Amphiphilic Peptide Nanoparticles for Biocompatible and Efficient Drug Delivery.

Self-assembled peptide nanostructures recently have gained much attention as drug delivery systems. As biomolecules, peptides have enhanced biocompatibility and biodegradability compared to polymer-based carriers. We introduce a peptide nanoparticle system containing arginine, histidine, and an enzyme-responsive core of repeating GLFG oligopeptides. GLFG oligopeptides exhibit specific sensitivity towards the enzyme cathepsin B that helps effective controlled release of cargo molecules in the cytoplasm. Arginine can induce cell penetration, and histidine facilitates lysosomal escape by its buffering capacity. Herein, we propose an enzyme-responsive amphiphilic peptide delivery system (Arg-His-(Gly-Phe-Lue-Gly)3, RH-(GFLG)3). The self-assembled RH-(GFLG)3 globular nanoparticle structure exhibited a positive charge and formulation stability for 35 days. Nile Red-tagged RH-(GFLG)3 nanoparticles showed good cellular uptake compared to the non-enzyme-responsive control groups with d-form peptides (LD (LRH-D(GFLG)3), DL (DRH-L(GFLG)3), and DD (DRH-D(GFLG)3). The RH-(GFLG)3 nanoparticles showed negligible cytotoxicity in HeLa cells and human RBCs. To determine the drug delivery efficacy, we introduced the anticancer drug doxorubicin (Dox) in the RH-(GFLG)3 nanoparticle system. LL-Dox exhibited formulation stability, maintaining the physical properties of the nanostructure, as well as a robust anticancer effect in HeLa cells compared to DD-Dox. These results indicate that the enzyme-sensitive RH-(GFLG)3 peptide nanoparticles are promising candidates as drug delivery carriers for biomedical applications.

Looking into a crystal ball: printing and patterning self-assembled peptide nanostructures.

The solution processability of organic semiconductors and conjugated polymers along with the advent of nanomaterials as conducting inks have revolutionized next-generation flexible consumer electronics. Another equally important class of nanomaterials, self-assembled peptides, heralded as next-generation materials for bioelectronics, have a lot of potential in printed technology. In this minireview, we address the self-assembly process in dipeptides, their application in electronics, and recent progress in three-dimensional printing. The prospect of a generalizable path for nanopatterning self-assembled peptides using ice lithography and its challenges are further discussed.

Beyond Tripeptides Two-Step Active Machine Learning for Very Large Data sets.

Self-assembling peptide nanostructures have been shown to be of great importance in nature and have presented many promising applications, for example, in medicine as drug-delivery vehicles, biosensors, and antivirals. Being very promising candidates for the growing field of bottom-up manufacture of functional nanomaterials, previous work (Frederix, et al. 2011 and 2015) has screened all possible amino acid combinations for di- and tripeptides in search of such materials. However, the enormous complexity and variety of linear combinations of the 20 amino acids make exhaustive simulation of all combinations of tetrapeptides and above infeasible. Therefore, we have developed an active machine-learning method (also known as “iterative learning” and “evolutionary search method”) which leverages a lower-resolution data set encompassing the whole search space and a just-in-time high-resolution data set which further analyzes those target peptides selected by the lower-resolution model. This model uses newly generated data upon each iteration to improve both lower- and higher-resolution models in the search for ideal candidates. Curation of the lower-resolution data set is explored as a method to control the selected candidates, based on criteria such as log P. A major aim of this method is to produce the best results in the least computationally demanding way. This model has been developed to be broadly applicable to other search spaces with minor changes to the algorithm, allowing its use in other areas of research.

Self-assembled peptide and protein nanostructures for anti-cancer therapy: Targeted delivery, stimuli-responsive devices and immunotherapy.

Self-assembled peptides and proteins possess tremendous potential as targeted drug delivery systems and key applications of these well-defined nanostructures reside in anti-cancer therapy. Peptides and proteins can self-assemble into nanostructures of diverse sizes and shapes in response to changing environmental conditions such as pH, temperature, ionic strength, as well as host and guest molecular interactions; their countless benefits include good biocompatibility and high loading capacity for hydrophobic and hydrophilic drugs. These self-assembled nanomaterials can be adorned with functional moieties to specifically target tumor cells. Stimuli-responsive features can also be incorporated with respect to the tumor microenvironment. This review sheds light on the growing interest in self-assembled peptides and proteins and their burgeoning applications in cancer treatment and immunotherapy.

Magneto-responsive hydrogels by self-assembly of low molecular weight peptides and crosslinking with iron oxide nanoparticles.

Hydrogels that respond to non-invasive, external stimuli such as a magnetic field are of exceptional interest for the development of adaptive soft materials. To date magneto tuneable gels are predominantly based on macromolecular building blocks, while comparable low molecular weight systems are rarely found in the literature. Herein, we report a highly efficient peptide-based gelator (Nap GFYE), which can form hydrogels and incorporate Fe3O4 superparamagnetic nanoparticles in the gel matrix. The magnetic nanoparticles act as a physical crosslinker for the self-assembled peptide nanostructures and thus give rise to a fortified hybrid gel with distinctively improved mechanical properties. Furthermore, the particles provide the material with magnetic susceptibility and a gel to sol transition is observed upon application of a weak magnetic field. Magnetization of the inorganic-organic hybrid nanomaterial leads to on-demand release of an incorporated fluorescent dye into the supernatant.

Pathway-Dependent Preferential Selection and Amplification of Variable Self-Assembled Peptide Nanostructures and Their Biological Activities.

We demonstrate the formation of diverse peptide nanostructures, which are "out of equilibrium" based on a single dipeptide gelator. These structures represent the differential energy states of the free energy landscape, which are accessed by differential energy inputs provided by variable self-assembly pathways, that is, heat-cool method or ultrasonication. A higher energy input by the heat-cool method created a thermodynamically favored long entangled nanofibrillar network, while twisted ribbonlike structures were prevalent by ultrasonication. Interestingly, the nanofibrillar network representing the global thermodynamic minima could be accessed by simply melting the kinetically trapped structures as indicated by the thermoreversibility studies. The impact on the material strength was remarkable; gels with an order of magnitude difference in mechanical properties could be fabricated by simply modulating the self-assembly pathways. Interestingly, the thermodynamically favored nanofibrous network promoted cellular adhesion and survival, while a significant number of cells fail to adhere on the kinetically trapped twisted ribbons. Thus, nonequilibrium nanostructures open up new directions to develop advanced functional materials with diverse functions.

Thermally Induced Structural Transition of Peptide Nanofibers into Nanoparticles with Enhanced Fluorescence Properties.

A heating treatment method for the synthesis of fluorescent nanoparticles using simple N-(9-fluorenylmethoxycarbonyl) (Fmoc)-protected tripeptides is reported. Two pairs of Fmoc-protected tripeptides (Fmoc-FR1 R2 , R1 =F or W, R2 =H or Y) were designed by changing the amino acid sequences of the peptides. The peptides can self-assemble into nanofibers at lower temperatures, which will spontaneously transform into fluorescent nanoparticles under heating treatment. Moreover, the fluorescence properties of the self-assembled structures can be affected by changing amino acids in the middle of the tripeptide. Specifically, tryptophan (W) can promote fluorescence of the assemblies incubated at high temperatures. Thus, the temperatures and amino sequences of the Fmoc-protected tripeptides have significant effects on the fluorescence of the assembled nanostructures. The results provide a design principle for self-assembled fluorescent peptide nanostructures with potential biomedical applications.

Self-Assembled Peptide Nanotube Films with High Proton Conductivity

Design flexibility and modularity have emerged as powerful tools in the development of functional self-assembled peptide nanostructures. In particular, the tendency of peptides to form fibrils and nanotubes has motivated the investigation of electron and, more recently, proton transport in their fibrous films. In this study, we present a detailed characterization by impedance spectroscopy of films of self-assembled cyclic octa-d,l-α-peptide self-assembled nanotubes with amine side chains that promote proton transport. We show that the conductivity of the peptide nanotube film, which is in the range of 0.3 mS cm-1, is within the same order of magnitude as that of ultrathin films of Nafion, a benchmark proton conducting polymer. In addition, we show that while slow diffusion processes at the interface are present for both films, additional interface effects occur in the peptide nanotube films at the same rate as their bulk proton transport effects, further limiting charge transport at the interface. Overall, our studies demonstrate the great potential of using peptides as building blocks for the preparation of bioinspired supramolecular proton conducting polymers with improved conductivity with respect to that of natural systems.

Self-Assembled Peptide Nanostructures for Photoelectrochemical Bioanalysis Application: A Proof-of-Concept Study.

Currently, one of important research directions of photoelectrochemical (PEC) bioanalysis is to exploit innovative photoactive species and their elegant implementations for selective detection and signal transduction. Different from existing candidates for photoelectrode development, this study, exemplified by the cationic dipeptide nanoparticles (CDNPs), reports the first demonstration of self-assembled peptide nanostructures (SAPNs) for the PEC bioanalysis. Specifically, the CDNPs were prepared as representative materials and then immobilized onto the indium tin oxide (ITO) electrode for the PEC differentiation of several commonly involved biomolecules such as ascorbic acid (AA) and l-cysteine. Significantly, the experimental results disclosed that the CDNPs possessed unique photocathodic responses and good analytical performance toward AA detection in terms of rapid response, high stability, and excellent selectivity. This work demonstrates the great potential of the large SAPN family for the future PEC bioanalysis development and has not been reported to our knowledge.

Amino acid conformations control the morphological and chiral features of the self-assembled peptide nanostructures: Young investigators perspective

HypothesisA variety of nanostructures with different chiral features can be self-assembled from short peptides with highly similar sequences. We hypothesize that these supramolecular nanostructures are ruled by the constituent amino acid residues which adopt their conformations under the influence of intra-/inter-molecular interactions during peptide self-assembly. ApproachThrough reviewing recent advances in the self-assembly of short peptides and focusing on the relationship between amino acid conformations, peptide secondary structures and intra-/inter-molecular interactions within the supramolecular architectures, we aim to rationalize the complex interactive processes involved in the self-assembly of short, designed peptides. ResultsGiven the highly complexing interactive processes, the adoption of amino acid conformations and their control over peptide self-assembly consist of 4 main steps: (1) Each amino acid residue adopts its unique conformation in a specific sequence; (2) The sequence exhibits its own main chain geometry and determines the propensity of the intermolecular alignment within the building block; (3) The structural propensity of the building block and the packing mode between them determine the self-assembled structural features such as twisting, growth and chirality; (4) In addition to intra-/inter-molecular interactions, inter-sheet and inter-building block interactions could also affect the residue conformations and nanostructures, causing structural readjustment.

Platinum-Ion-Mediated Self-Assembly of Hairpin Peptides and Synthesis of Platinum Nanostructures.

Nanostructures and nanomaterials based on peptide self-assembly have attracted tremendous interests due to the functionalities of peptide molecules. Furthermore, the self-assembled peptide nanostructures are also adopted to fabricate nanomaterials and nanodevices. In this work, the intramolecular folding and self-assembly of a β-hairpin peptide CBHH were first studied under the regulation of platinum ion. And then, platinum nanostructures were synthesized through the reduction of platinum ions templated with peptide self-assemblies. The results of circular dichroism spectroscopy, UV-vis spectroscopy, isothermal titration calorimetry, and atomic force microscopy observation showed that platinum ions could promote the conversion of peptide CBHH secondary structure from a random coil to a β-sheet through coordination with histidine residues. Platinum nanostructures including nanorods and one dimensionally aligned nanorods were synthesized through in situ reduction with CBHH self-assembled nanofiber as the templates. And the synthesized platinum nanostructures showed excellent electrocatalytic activities.

Novel Materials From the Supramolecular Self-Assembly of Short Helical β3-Peptide Foldamers.

Self-assembly is the spontaneous organization of small components into higher-order structures facilitated by the collective balance of non-covalent interactions. Peptide-based self-assembly systems exploit the ability of peptides to adopt distinct secondary structures and have been used to produce a range of well-defined nanostructures, such as nanotubes, nanofibres, nanoribbons, nanospheres, nanotapes, and nanorods. While most of these systems involve self-assembly of α-peptides, more recently β-peptides have also been reported to undergo supramolecular self-assembly, and have been used to produce materials—such as hydrogels—that are tailored for applications in tissue engineering, cell culture and drug delivery. This review provides an overview of self-assembled peptide nanostructures obtained via the supramolecular self-assembly of short β-peptide foldamers with a specific focus on N-acetyl-β3-peptides and their applications as bio- and nanomaterials.