Artificial self-assemblies are known to fold into amyloid-like fibrillar structures with properties that are quite similar to those formed in vivo or in Nature. Therefore, these systems can give insights how to mimic Nature, and then develop it for applicable technologies. Moreover, using short synthetic peptides aids interpretation of structural details compared to the more complex and large naturally occurring amyloidogenic proteins/peptides. Two models of a-amino acids short peptides have been used here to mimic Nature. The first is based on the design KFFEAAAKKFE which has been previously characterised and shown to form an amyloid-like structure with cross-b architecture. It is utilised here for the first time to template silica from the precursor tetraexthoxy orthosilcate. Results reveal that variant peptides are able to form silica-nanowire suprastructures where Arg and Lys play a fundamental role in controlling silica nucleation, polymerisation and shaping the final suprastructure morphology. Furthermore, the silica-nanowires retained the cross-b core even after treating with harsh conditions, which point to their exceptional stability for multiple potential applications. The second model based on the design Ac-IHIHIQI-CONH2 has been previously used to mimic the natural carbonic anhydrase where it coordinated a metal ion (Zn+2) to catalyse a hydrolysing reaction of the substrate p-nitrophenyl acetate. This design is developed here and structurally characterised for the first time to reveal amyloid-like fibrils with cross-b hierarchy, and displays an excellent propensity to mimic carbonic anhydrase. Moreover, results indicated that this activity is governed by a few things: side chains-dependency where alternating His and Ile at position i, i+2 with Tyr at position 6 was the most active design while incorporating Glu at position 5 indicated the lower activity; Zn-dependency, protecting ends-dependency; and temperature and fibril age-dependency. The third model is based on tri- and hexa- peptides that have b-amino acids as a structural unit. These are decorated with functional groups and designed to self-assemble via hydrogen-bonding between amide groups at position i. i+2 into a helical secondary structure. They have been structurally characterised here for the first time, and results revealed that the designed peptides form different morphologies and structural variations depending on the position of the functional group and the sequence. Controlling the balance for all these designs may be adapted for specific properties to be efficient in multiple nanobiotechnological applications.

Many peptides self-assemble to form amyloid fibrils. We previously explored the sequence propensity to form amyloid using variants of a designed peptide with sequence KFFEAAAKKFFE. These variant peptides form highly stable amyloid fibrils with varied lateral assembly and are ideal to template further assembly of non-proteinaceous material. Herein, we show that the fibrils formed by peptide variants can be coated with a layer of silica to produce silica nanowires using tetraethyl-orthosilicate. The resulting nanowires were characterized using electron microscopy (TEM), X-ray fiber diffraction, FTIR and cross-section EM to reveal a nanostructure with peptidic core. Lysine residues play a role in templating the formation of silica on the fibril surface and, using this library of peptides, we have explored the contributions of lysine as well as arginine to silica templating, and find that sequence plays an important role in determining the physical nature and structure of the resulting nanowires.

Natural biological enzymes possess catalytic sites that are generally surrounded by a large three-dimensional scaffold. However, the proportion of the protein molecule that participates in the catalytic reaction is relatively small. The generation of artificial or miniature enzymes has long been a focus of research because enzyme mimetics can be produced with high activity at low cost. These enzymes aim to mimic the active sites without the additional architecture contributed by the protein chain. Previous work has shown that amyloidogenic peptides are able to self-assemble to create an active site that is capable of binding zinc and catalysing an esterase reaction. Here, we describe the structural characterisation of a set of designed peptides that form an amyloid-like architecture and reveal that their capability to mimic carbonic anhydrase and serve as enzyme-like catalysts is related to their ability to self-assemble. These amyloid fibril structures can bind the metal ion Zn2+ via a three-dimensional arrangement of His residues created by the amyloid architecture. Our results suggest that the catalytic efficiency of amyloid-like assembly is not only zinc-dependent but also depends on an active centre created by the peptides which is, in turn, dependent on the ordered architecture. These fibrils have good esterase activity, and they may serve as good models for the evolution of modern-day enzymes. Furthermore, they may be useful in designing self-assembling fibrils for applications as metal ion catalysts. This study also demonstrates that the ligands surrounding the catalytic site affect the affinity of the zinc-binding site to bind the substrate contributing to the enzymatic activity of the assembled peptides.

Background: A series of amyloidogenic peptides based on the sequence KFFEAAAKKFFE template the silica precursor, tetraethyl orthosilicate to form silica-nanowires containing a cross-β peptide core.

Results: Investigation of the stability of these fibres reveals that the silica layers protect the silica-nanowires allowing them to maintain their shape and physical and chemical properties after incubation with organic solvents such as 2-propanol, ethanol, and acetonitrile, as well as in a strong acidic solution at pH 1.5. Furthermore, these nanowires were thermally stable in an aqueous solution when heated up to 70 °C, and upon autoclaving. They also preserved their conformation following incubation up to 4 weeks under these harsh conditions, and showed exceptionally high physical stability up to 1000 °C after ageing for 12 months. We show that they maintain their β-sheet peptide core even after harsh treatment by confirming the β-sheet content using Fourier transform infrared spectra. The silica nanowires show significantly higher chemical and thermal stability compared to the unsiliconised fibrils.

Conclusions: The notable chemical and thermal stability of these silica nanowires points to their potential for use in microelectromechanics processes or fabrication for nanotechnological devices.

Many peptides self-assemble to form amyloid fibrils. We previously explored the sequence propensity to form amyloid using variants of a designed peptide with sequence KFFEAAAKKFFE. These variant peptides form highly stable amyloid fibrils with varied lateral assembly and are ideal to template further assembly of non-proteinaceous material. Herein, we show that the fibrils formed by peptide variants can be coated with a layer of silica to produce silica nanowires using tetraethyl-orthosilicate. The resulting nanowires were characterized using electron microscopy (TEM), X-ray fiber diffraction, FTIR and cross-section EM to reveal a nanostructure with peptidic core. Lysine residues play a role in templating the formation of silica on the fibril surface and, using this library of peptides, we have explored the contributions of lysine as well as arginine to silica templating, and find that sequence plays an important role in determining the physical nature and structure of the resulting nanowires.