Molecular self-assembly using peptide nucleic acids

Fabrication strategies for chiral self-assembly surface

Chiral self-assembly is the spontaneous organization of individual building blocks from chiral (bio)molecules to macroscopic objects into ordered superstructures. Chiral self-assembly is ubiquitous in nature, such as DNA and proteins, which formed the foundation of biological structures. In addition to chiral (bio) molecules, chiral ordered superstructures constructed by self-assembly have also attracted much attention. Chiral self-assembly usually refers to the process of forming chiral aggregates in an ordered arrangement under various non-covalent bonding such as H-bond, π-π interactions, van der Waals forces (dipole-dipole, electrostatic effects, etc.), and hydrophobic interactions. Chiral assembly involves the spontaneous process, which followed the minimum energy rule. It is essentially an intermolecular interaction force. Self-assembled chiral materials based on chiral recognition in electrochemistry, chiral catalysis, optical sensing, chiral separation, etc. have a broad application potential with the research development of chiral materials in recent years.

Recent advancements in bionanomaterial applications of peptide nucleic acid assemblies

Peptide nucleic acid (PNA) is a unique combination of peptides and nucleic acids. PNA can exhibit hydrogen bonding interactions with complementary nucleobases like DNA/RNA. Also, its polyamide backbone allows easy incorporation of biomolecules like peptides and proteins to build hybrid molecular constructs. Because of chimeric structural properties, PNA has lots of potential to build diverse nanostructures. However, progress in the PNA material field is still immature compared with its massive applications in antisense oligonucleotide research. Examples of well-defined molecular assemblies have been reported with PNA amphiphiles, self-assembling guanine-PNA monomers/dimers, and PNA-decorated nucleic acids/ polymers/ peptides. All these works indicate the great potential of PNA to be used as bionanomaterials. The review summarizes the recent reports on PNA-based nanostructures and their versatile applications. Additionally, this review shares a perspective to promote a better understanding of controlling molecular assembly by the systematic structural modifications of PNA monomers.

A highly sensitive and robust electrochemical biosensor for microRNA detection based on PNA-DNA hetero-three-way junction formation and target-recycling catalytic hairpin assembly amplification

Robust and sensitive methods for the detection of microRNAs (miRNAs) are crucial in the clinical diagnosis of cancers. In this study, a novel electrochemical biosensor with high sensitivity for miRNA-21 detection is developed, which relies on the formation of a peptide nucleic acid (PNA)-DNA hetero-three-way junction (H3WJ) and target-recycling catalytic hairpin assembly (CHA) amplification. The electroneutral PNA probes are initially immobilized onto a gold electrode to construct the sensor. Upon introduction of miRNA-21, target-recycling CHA is initiated, resulting in abundant double-stranded CHA products. Subsequently, association between the PNA probes and these products leads to the formation of PNA-DNA H3WJs. Consequently, the electrode surface is densely populated with numerous electroactive Ferrocene (Fc) groups, resulting in a significantly amplified current response for highly sensitive detection of miRNA-21 at concentrations as low as 0.15 fM. This approach demonstrates remarkable specificity towards target miRNAs and can be utilized for quantitative monitoring of miRNA-21 expression in human cancer cells. More importantly, the sensor exhibits exceptional stability and shows a significant reduction in background noise during miRNA detection, making this method a highly promising sensing platform for monitoring various miRNA biomarkers to facilitate the diagnosis of diverse cancers.

Tryptophan-PNA gc Conjugates Self-Assemble to Form Fibers

Peptide nucleic acids and their conjugates to peptides can self-assemble and generate complex architectures. In this work, we explored the self-assembly of PNA dimers conjugated to the dipeptide WW. Our studies suggest that the indole ring of tryptophan promotes aggregation of the conjugates. The onset of fluorescence is observed upon self-assembly. The structure of self-assembled WWgc is concentration-dependent, being spherical at low concentrations and fibrous at high concentrations. As suggested by molecular modeling studies, fibers are stabilized by stacking interactions between tryptophans and Watson-Crick hydrogen bonds between nucleobases.

Intrinsic fluorescence of nucleobase crystals

Nucleobase crystals demonstrate unique intrinsic fluorescence properties in the visible spectral range. This is in contrast to their monomeric counterparts. Moreover, some nucleobases were found to exhibit red edge excitation shift. This behavior is uncommon in the field of organic supramolecular materials and could have implications in fields such as therapeutics of metabolic disorders and materials science.

Solvent modulation in peptide sub-microfibers obtained by solution blow spinning

Peptides possess high chemical diversity at the amino acid sequence level, which further translates into versatile functions. Peptides with self-assembling properties can be processed into diverse formats giving rise to bio-based materials. Peptide-based spun fibers are an interesting format due to high surface-area and versatility, though the field is still in its infancy due to the challenges in applying the synthetic polymer spinning processes to protein fibers to peptides. In this work we show the use of solution blow-spinning to produce peptide fibers. Peptide fiber formation was assisted by the polymer poly (vinyl pyrrolidone) (PVP) in two solvent conditions. Peptide miscibility and further self-assembling propensity in the solvents played a major role in fiber formation. When employing acetic acid as solvent, peptide fibers (0.5 μm) are formed around PVP fibers (0.75 μm), whereas in isopropanol only one type of fibers are formed, consisting of mixed peptide and PVP (1 μm). This report highlights solvent modulation as a mean to obtain different peptide sub-microfibers via a single injection nozzle in solution blow spinning. We anticipate this strategy to be applied to other small peptides with self-assembly propensity to obtain multi-functional proteinaceous fibers.

Artificial genetic polymers against human pathologies

Originally discovered by Nielsen in 1991, peptide nucleic acids and other artificial genetic polymers have gained a lot of interest from the scientific community. Due to their unique biophysical features these artificial hybrid polymers are now being employed in various areas of theranostics (therapy and diagnostics). The current review provides an overview of their structure, principles of rational design, and biophysical features as well as highlights the areas of their successful implementation in biology and biomedicine. Finally, the review discusses the areas of improvement that would allow their use as a new class of therapeutics in the future.

Nucleic acid nanoassembly-enhanced RNA therapeutics and diagnosis

RNAs are involved in the crucial processes of disease progression and have emerged as powerful therapeutic targets and diagnostic biomarkers. However, efficient delivery of therapeutic RNA to the targeted location and precise detection of RNA markers remains challenging. Recently, more and more attention has been paid to applying nucleic acid nanoassemblies in diagnosing and treating. Due to the flexibility and deformability of nucleic acids, the nanoassemblies could be fabricated with different shapes and structures. With hybridization, nucleic acid nanoassemblies, including DNA and RNA nanostructures, can be applied to enhance RNA therapeutics and diagnosis. This review briefly introduces the construction and properties of different nucleic acid nanoassemblies and their applications for RNA therapy and diagnosis and makes further prospects for their development.

Head on Comparison of Self- and Nano-assemblies of Gamma Peptide Nucleic Acid Amphiphiles

Peptide nucleic acids (PNAs) are nucleic acid analogs with superior hybridization properties and enzymatic stability than deoxyribonucleic acid (DNA). In addition to gene targeting applications, PNAs have garnered significant attention as bio-polymer due to the Watson-Crick -based molecular recognition and flexibility of synthesis. Here, we engineered PNA amphiphiles using chemically modified gamma PNA (8 mer in length) containing hydrophilic diethylene glycol units at the gamma position and covalently conjugated lauric acid (C12) as a hydrophobic moiety. Gamma PNA (γPNA) amphiphiles self-assemble into spherical vesicles. Further, we formulate nano-assemblies using the amphiphilic γPNA as a polymer via ethanol injection-based protocols. We perform comprehensive head-on comparison of the physicochemical and cellular uptake properties of PNA derived self- and nano-assemblies. Small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) analysis reveal ellipsoidal morphology of γPNA nano-assemblies that results in superior cellular delivery compate to the spherical self-assembly. Next, we compare the functional activities of γPNA self-and nano-assemblies in lymphoma cells via multiple endpoints, including gene expression, cell viability, and apoptosis-based assays. Overall, we establish that γPNA amphiphile is a functionally active bio-polymer to formulate nano-assemblies for a wide range of biomedical applications.

Depsipeptide Nucleic Acids: Prebiotic Formation, Oligomerization, and Self-Assembly of a New Proto-Nucleic Acid Candidate

The mechanism by which informational polymers first formed on the early earth is currently unknown. The RNA world hypothesis implies that RNA oligomers were produced prebiotically, before the emergence of enzymes, but the demonstration of such a process remains challenging. Alternatively, RNA may have been preceded by an earlier ancestral polymer, or proto-RNA, that had a greater propensity for self-assembly than RNA, with the eventual transition to functionally superior RNA being the result of chemical or biological evolution. We report a new class of nucleic acid analog, depsipeptide nucleic acid (DepsiPNA), which displays several properties that are attractive as a candidate for proto-RNA. The monomers of depsipeptide nucleic acids can form under plausibly prebiotic conditions. These monomers oligomerize spontaneously when dried from aqueous solutions to form nucleobase-functionalized depsipeptides. Once formed, these DepsiPNA oligomers are capable of complementary self-assembly and are resistant to hydrolysis in the assembled state. These results suggest that the initial formation of primitive, self-assembling, informational polymers on the early earth may have been relatively facile if the constraints of an RNA-first scenario are relaxed.

Molecular Assembly of Triplex of Duplexes from Homothyminyl-Homocytosinyl Cγ(S/R)-Bimodal Peptide Nucleic Acids with dA8/dG6 and the Cell Permeability of Bimodal Peptide Nucleic Acids

Peptide nucleic acids (PNAs) are analogues of DNA with a neutral acyclic polyamide backbone containing nucleobases attached through a t-amide link on repeating units of aminoethylglycine (aeg). They bind to complementary DNA or RNA in a sequence-specific manner to form duplexes with higher stablity than DNA:DNA and DNA:RNA hybrids. We have recently explored a new type of PNA termed bimodal PNA (bm-PNA) designed with two nucleobases per aeg repeating unit of PNA oligomer and attached at Cα or Cγ of each aeg unit through a spacer sidechain. We demonstrated that Cγ-bimodal PNA oligomers with mixed nucleobase sequences bind concurrently two different complementary DNAs, forming double duplexes, one from each t-amide and Cγ face, sharing a common PNA backbone. In such bm-PNA:DNA ternary complexes, the two duplexes show higher thermal stability than individual duplexes. Herein, we show that Cγ(S/R)-bimodal PNAs with homothymines (T8) on a t-amide face and homocytosine (C6) on a Cγ-face form a conjoined pentameric complex consisting of a triplex (bm-PNA-T8)2:dA8 and two duplexes of bm-PNA-C6:dG6. The pentameric complex [dG6:Cγ(S/R)-bm-PNA:dA8:Cγ(S/R)-bm-PNA:dG6] exhibits higher thermal stability than the individual triplex and duplex, with Cγ(S)-bm-PNA complexes being more stable than Cγ(R)-bm-PNA complexes. The conjoined duplexes of Cγ-bimodal PNAs can be used to generate novel higher-order assemblies with DNA and RNA. The Cγ(S/R)-bimodal PNAs are shown to enter MCF7 and NIH 3T3 cells and exhibit low toxicity to cells.

Direct and Efficient Conjugation of Quantum Dots to DNA Nanostructures with Peptide-PNA

DNA nanotechnology has proven to be a powerful strategy for the bottom-up preparation of colloidal nanoparticle (NP) superstructures, enabling the coordination of multiple NPs with orientation and separation approaching nanometer precision. To do this, NPs are often conjugated with chemically modified, single-stranded (ss) DNA that can recognize complementary ssDNA on the DNA nanostructure. The limitation is that many NPs cannot be easily conjugated with ssDNA, and other conjugation strategies are expensive, inefficient, or reduce the specificity and/or precision with which NPs can be placed. As an alternative, the conjugation of nanoparticle-binding peptides and peptide nucleic acids (PNA) can produce peptide-PNA with distinct NP-binding and DNA-binding domains. Here, we demonstrate a simple application of this method to conjugate semiconductor quantum dots (QDs) directly to DNA nanostructures by means of a peptide-PNA with a six-histidine peptide motif that binds to the QD surface. With this method, we achieved greater than 90% capture efficiency for multiple QDs on a single DNA nanostructure while preserving both site specificity and precise spatial control of QD placement. Additionally, we investigated the effects of peptide-PNA charge on the efficacy of QD immobilization in suboptimal conditions. The results validate peptide-PNA as a viable alternative to ssDNA conjugation of NPs and warrant studies of other NP-binding peptides for peptide-PNA conjugation.

Fluorinated peptide biomaterials

Fluorinated compounds, while rarely used by nature, are emerging as fundamental ingredients in biomedical research, with applications in drug discovery, metabolomics, biospectroscopy, and, as the focus of this review, peptide/protein engineering. Leveraging the fluorous effect to direct peptide assembly has evolved an entirely new class of organofluorine building blocks from which unique and bioactive materials can be constructed. Here, we discuss three distinct peptide fluorination strategies used to design and induce peptide assembly into nano-, micro-, and macrosupramolecular states that potentiate high-ordered organization into material scaffolds. These fluorine-tailored peptide assemblies employ the unique fluorous environment to boost biofunctionality for a broad range of applications, from drug delivery to antibacterial coatings. This review provides foundational tactics for peptide fluorination and discusses the utility of these fluorous-directed hierarchical structures as material platforms in diverse biomedical applications.

Gem-dimethyl peptide nucleic acid (α/β/γ-gdm-PNA) monomers: synthesis and the role of gdm-substituents in preferential stabilisation of Z/E-rotamers

The flexible backbone of aminoethylglycine (aeg) PNA upon substitution becomes sterically constrained to enable conformational pre-organization for preferential binding to DNA or RNA. The bulky gem-dimethyl (gdm) substituent on carbons adjacent to the t-amide sidechain either at Cα (glycyl) or Cβ/Cγ (aminoethylene) sides may influence the Z/E rotamer ratio arising from a restricted rotation around the t-amide bond. Employing 2D NMR (NOESY), it is shown here that the Cα-gdm-PNA-T monomer exhibits exclusively the Z-rotamer, while the Cβ-gdm-PNA-T monomer shows only the E-rotamer. The unsubstituted aeg-PNA-T and Cγ-gdm-PNA-T monomers display a mixture of Z/E rotamers. The rotamers with t-amide carbonyl pointing towards the gem-dimethyl group always prevailed. The results are supported by computational studies that suggested that the preferred rotamers are the outcome of a net energetic benefit from the stabilising n-π* interactions of carbonyls (amide backbone and t-amide sidechain), and C-HO interactions and the destabilising steric clash of gem-dimethyl groups with the t-amido methylene group. The E-rotamer structure in Cγ-gdm is also characterised by X-ray crystallography. The exclusive E-rotamer for the Cβ-gdm monomer seen in solution here is the first such example among several modified PNA monomers. Since the conformation of the sidechain is important for inducing base stacking and effective base pairing, the exclusive E-rotamer in the Cβ-gdm monomer may have significance in the properties of the derived PNA : DNA/RNA duplexes with all E-rotamers.

Supramolecular Assembly and Chirality of Synthetic Carbohydrate Materials

Hierarchical carbohydrate architectures serve multiple roles in nature. Hardly any correlations between the carbohydrate chemical structures and the material properties are available due to the lack of standards and suitable analytic techniques. Therefore, designer carbohydrate materials remain highly unexplored, as compared to peptides and nucleic acids. A synthetic D-glucose disaccharide, DD, was chosen as a model to explore carbohydrate materials. Microcrystal electron diffraction (MicroED), optimized for oligosaccharides, revealed that DD assembled into highly crystalline left-handed helical fibers. The supramolecular architecture was correlated to the local crystal organization, allowing for the design of the enantiomeric right-handed fibers, based on the L-glucose disaccharide, LL, or flat lamellae, based on the racemic mixture. Tunable morphologies and mechanical properties suggest the potential of carbohydrate materials for nanotechnology applications.

Silver assisted stereo-directed assembly of branched peptide nucleic acids into four-point nanostars

Branched chiral peptide nucleic acids br(4S/R)-PNA with three arms of PNA-C4 strands were constructed on a central chiral core of 4(R/S)-aminoproline as the branching center. The addition of Ag+ triggered the self-assembly of branched PNAs through the formation of C-Ag+-C metallo base pairing of the three PNA C4 arms leading to non-covalent dendrimers, whose architecture is directed by the C4(R/S)-stereocenter of core 4-aminoproline. The 4S-aminoprolyl core enabled the precise formation of four-pointed nanostars that was not realised with 4R-aminoprolyl or acyclic, achiral aminoethyl glycyl PNA cores. The dendritic assembly of 4 pointed nanostars exhibited net chirality of base stacks in CD spectra, while the base stack assembly from br(4R)-PNA 2 was overall achiral. The results demonstrate that the silver assisted, 4S-aminoproline core stereo selective chiral assembly of branched PNAs manifests into nanostar morphology. The chiral branched PNAs open new vistas in the supramolecular organization of nucleic acids.

Bioinspired Suprahelical Frameworks as Scaffolds for Artificial Photosynthesis

Framework materials have shown promising potential in various biological applications. However, the state-of-the-art components show low biocompatibility or mechanical instability, or cannot integrate both optics and electronics, thus severely limiting their extensive applications in biological systems. Herein, we demonstrate that amide-based bioorganic building blocks, including dipeptides and dipeptide nucleic acids, can self-assemble into hydrogen-bonded suprahelix architectures of controllable handedness, which then form suprahelical frameworks with diverse cavities. Especially, the cavities can be tuned to be hydrophilic or hydrophobic, and the shortest diagonal distance can be modulated from 0.5 to 1.8 nm, with the volume proportion in the unit cell changing from 5 to 60%. Furthermore, the hydrogen bonding networks result in high mechanical rigidity and semiconductively optoelectronic properties, which allow the utilization of the suprahelical frameworks as supramolecular scaffolds for artificial photosynthesis. Our findings reveal amide-based suprahelix architectures acting as bioinspired supramolecular frameworks, thus extending the constituents portfolio and increasing the feasibility of using framework materials for biological applications.

Peptide nucleic acids harness dual information codes in a single molecule

Nature encodes the information required for life in two fundamental biopolymers: nucleic acids and proteins. Peptide nucleic acid (PNA), a synthetic analog comprised of nucleobases arrayed along a pseudopeptide backbone, has the ability to combine the power of nucleic acids to encode information with the versatility of amino acids to encode structure and function. Historically, PNA has been perceived as a simple nucleic acid mimic having desirable properties such as high biostability and strong affinity for complementary nucleic acids. In this feature article, we aim to adjust this perception by highlighting the ability of PNA to act as a peptide mimic and showing the largely untapped potential to encode information in the amino acid sequence. First, we provide an introduction to PNA and discuss the use of conjugation to impart tunable properties to the biopolymer. Next, we describe the integration of functional groups directly into the PNA backbone to impart specific physical properties. Lastly, we highlight the use of these integrated amino acid side chains to encode peptide-like sequences in the PNA backbone, imparting novel activity and function and demonstrating the ability of PNA to simultaneously mimic both a peptide and a nucleic acid.

Self-Assembly of Diphenylalanine-Peptide Nucleic Acid Conjugates

The synthesis and self-assembled nanostructures of a series of nucleopeptides (NPs) derived from the dipeptide Phe-Phe and the peptide nucleic acid unit which are covalently attached through an amide or a triazole linker are described. Depending on the variables such as protecting groups, linkers, and nucleobases, spherical nanoparticles were observed through scanning electron microscopy and high-resolution transmission electron microscopy images, and the porous nature of representative NPs was corroborated by carboxyfluorescein entrapment. Hydrophobic substituents on different sites of NPs and solvents employed for peptide self-assembly played a crucial role for corresponding morphologies. The stability of nanoparticles was also probed under external stimuli such as pH, temperature, and enzymatic hydrolysis using proteolytic enzymes. The semiconducting nature of the NP-modified carbon electrodes suggested their potential use as a new capacitor material.

Impact of N-(2-aminoethyl) Glycine Unit on Watson-Crick Base Pairs

We aim to understand the structure and stability of the backbone tailored Watson-Crick base pairs, Guanine-Cytosine (GC), Adenine-Thymine (AT) and Adenine-Uracil (AU) by incorporating N-(2-aminoethyl) glycine units (linked by amide bonds) at the purine and pyrimidine sites of the nucleobases. Density functional theory (DFT) is employed in which B3LYP/6-311++G∗ ∗ level of theory has been used to optimize all the structures. The peptide attached base pairs are compared with the natural deoxyribose nucleic acid (DNA)/ribonucleic acid (RNA) base pairs and the calculations are carried out in both the gas and solution phases. The structural propensities of the optimized base pairs are analyzed using base pair geometries, hydrogen bond distances and stabilization energies and, compared with the standard reference data. The structural parameters were found to correlate well with the available data. The addition of peptide chain at the back bone of the DNA/RNA base pairs results only with a minimal distortion and hence does not alter the structural configuration of the base pairs. Also enhanced stability of the base pairs is spotted while adding peptidic chain at the purine site rather than the pyrimidine site of the nucleobases. The stability of the complexes is further interpreted by considering the hydrogen bonded N–H stretching frequencies of the respective base pairs. The discrimination in the interaction energies observed in both gas and solution phases are resulted due to the existence of distinct lowest unoccupied molecular orbitals (LUMO) in the solution phase. The reactivity of the base pairs is also analyzed through the in-depth examinations on the highest occupied molecular orbital (HOMO)-LUMO orbitals.

A self-assembly study of PNA-porphyrin and PNA-BODIPY hybrids in mixed solvent systems

In this work a peptide nucleic acid (PNA) was covalently connected with two different chromophores, namely porphyrin and boron-dipyrromethene. To the best of our knowledge, this is the first example in the literature where a PNA unit is covalently linked to such chromophores. The self-assembly properties of the hybrids were examined through electron microscopy experiments by adopting the "good-bad" solvent self-assembly protocol. For both hybrids (PNA-TPP and PNA-BDP) we were able to observe distinctive supramolecular architectures. During these studies we investigated the influence of the solvent system, the concentration and the deposition method on the morphology of the formed nanostructures. In the case of PNA-TPP under all examined conditions well-formed nanospheres were obtained. Interestingly, in the PNA-BDP hybrid by simply altering the solvent mixture, self-assemblies of two different morphologies were formed (spherical and flake shaped). Absorption and emission studies suggested the formation of J-aggregates in all the obtained nanostructures. The nano-architectures assembled by PNA conjugates are capable of light-harvesting and producing hydrogen using Pt nanoparticles as a photocatalyst.

The cardioprotective effect of dexrazoxane (Cardioxane) is consistent with sequestration of poly(ADP-ribose) by self-assembly and not depletion of topoisomerase 2B

Following systematic scrutiny of the evidence in support of the hypothesis that the cardioprotective mechanism of action of dexrazoxane is mediated by a 'depletion' or 'downregulation' of Top2β protein levels in heart tissue, the author concludes that this hypothesis is untenable. In seeking to understand how dexrazoxane protects the heart, the outcomes of a customised association rule learning algorithm incorporating the use of antecedent surrogate variables (CEME, 2017 McCormack Pharma) reveal a previously unknown relationship between dexrazoxane and poly(ADP-ribose) (PAR) polymer. The author shows how this previously unknown relationship explains both acute and long-term cardioprotection in patients receiving anthracyclines. In addition, as a direct inhibitor of PAR dexrazoxane has access to the epigenome and this offers a new insight into protection by dexrazoxane against doxorubicin-induced late-onset damage [McCormack K, manuscript in preparation]. Notably, through this review article, the author illustrates the practical application of probing natural language text using an association rule learning algorithm for the discovery of new and interesting associations that, otherwise, would remain lost. Historically, the use of CEME enabled the first report of the capacity of a small molecule to catalyse the hybrid self-assembly of a nucleic acid biopolymer via canonical and non-canonical, non-covalent interactions analogous to Watson Crick and Hoogsteen base pairing, respectively.

Orthogonal γPNA Dimerization Domains Empower DNA Binders with Cooperativity and Versatility Mimicking that of Transcription Factor Pairs

Synthetic molecules capable of DNA binding and mimicking cooperation of transcription factor (TF) pairs have long been considered a promising tool for manipulating gene expression. Our previously reported Pip-HoGu system, a programmable DNA binder pyrrole-imidazole polyamides (PIPs) conjugated to host-guest moiety, defined a general framework for mimicking cooperative TF pair-DNA interactions. Here, we supplanted the cooperation modules with left-handed (LH) γPNA modules: i.e., PIPs conjugated with nucleic acid-based cooperation system (Pip-NaCo). LH γPNA was chosen because of its bioorthogonality, sequence-specific interaction, and high binding affinity toward the partner strand. From the results of the Pip-NaCo system, cooperativity is highly comparable to the natural TF pair-DNA system, with a minimum energetics of cooperation of -3.27 kcal mol-1 . Moreover, through changing the linker conjugation site, binding mode, and the length of γPNAs sequence, the cooperative energetics of Pip-NaCo can be tuned independently and rationally. The current Pip-NaCo platform might also have the potential for precise manipulation of biological processes through the construction of triple to multiple heterobinding systems.

Amphiphilic peptides as novel nanomaterials: design, self-assembly and application

Designer self-assembling peptides are a category of emerging nanobiomaterials which have been widely investigated in the past decades. In this field, amphiphilic peptides have received special attention for their simplicity in design and versatility in application. This review focuses on recent progress in designer amphiphilic peptides, trying to give a comprehensive overview about this special type of self-assembling peptides. By exploring published studies on several typical types of amphiphilic peptides in recent years, herein we discuss in detail the basic design, self-assembling behaviors and the mechanism of amphiphilic peptides, as well as how their nanostructures are affected by the peptide characteristics or environmental parameters. The applications of these peptides as potential nanomaterials for nanomedicine and nanotechnology are also summarized.

Reductionist Approach in Peptide-Based Nanotechnology

The formation of ordered nanostructures by molecular self-assembly of proteins and peptides represents one of the principal directions in nanotechnology. Indeed, polyamides provide superior features as materials with diverse physical properties. A reductionist approach allowed the identification of extremely short peptide sequences, as short as dipeptides, which could form well-ordered amyloid-like β-sheet-rich assemblies comparable to supramolecular structures made of much larger proteins. Some of the peptide assemblies show remarkable mechanical, optical, and electrical characteristics. Another direction of reductionism utilized a natural noncoded amino acid, α-aminoisobutryic acid, to form short superhelical assemblies. The use of this exceptional helix inducer motif allowed the fabrication of single heptad repeats used in various biointerfaces, including their use as surfactants and DNA-binding agents. Two additional directions of the reductionist approach include the use of peptide nucleic acids (PNAs) and coassembly techniques. The diversified accomplishments of the reductionist approach, as well as the exciting future advances it bears, are discussed.

Geometric Principles for Designing Highly Symmetric Self-Assembling Protein Nanomaterials

Emerging protein design strategies are enabling the creation of diverse, self-assembling supramolecular structures with precision on the atomic scale. The design possibilities include various types of architectures: finite cages or shells, essentially unbounded two-dimensional and three-dimensional arrays (i.e., crystals), and linear or tubular filaments. In nature, structures of those types are generally symmetric, and, accordingly, symmetry provides a powerful guide for developing new design approaches. Recent design studies have produced numerous protein assemblies in close agreement with geometric specifications. For certain design approaches, a complete list of allowable symmetry combinations that can be used for construction has been articulated, opening a path to a rich diversity of geometrically defined protein materials. Future challenges include improving and elaborating on current strategies and endowing designed protein nanomaterials with properties useful in nanomedicine and material science applications.