Thermo-Chemical Cues-Mediated Strategy to Control Peptide Self-Assembly and Charge Transfer Complexation.

Peptide amphiphiles (PAs) are known for their remarkable ability to undergo molecular self-assembly, a process that is highly responsive to the local microenvironment. Herein, we design a pyrene tethered peptide amphiphile Py-VFFAKK, 1 that exhibits pathway-driven self-assembly from metastable nanoparticles to kinetically controlled nanofibers and thermodynamically stable twisted bundles upon modulations in pH, temperature, and chemical cues. The presence of the pyrene moiety ensures donation of the electron to an electron acceptor, namely, 7,7,8,8-tetracyanoquinodimethane (TCNQ), to form a supramolecular charge transfer complex in aqueous solution that was studied in detail with microscopic and spectroscopic techniques. Excitation of the donor species in its excimer state facilitates electron donation to the acceptor moiety, paving away a long-lived charge-separated state that persists for over a nanosecond, as ascertained through transient absorption spectroscopy. Finally, the self-assembled charge transfer complex is explored toward antimicrobial properties with Escherichia coli while maintaining biocompatibility toward L929 mice fibroblast cells.

Use of discarded corneo-scleral rims to create cornea-like tissue.

BACKGROUND: Corneal disease is a major cause of blindness. Transplantation of cadaver-derived corneas (keratoplasty) is still the current therapy of choice; however, the global shortage of donor corneas continues to drive a search for alternatives. To this end, biosynthetic corneal substitutes have recently begun to gain importance. Here, we present a novel method for the generation of a cornea-like tissue (CLT), using corneo-scleral rims discarded after keratoplasty. METHODS AND RESULTS: Type I collagen was polymerized within the corneo-scleral rim, which functioned as a 'host' mould, directing the 'guest' collagen to polymerize into disc-shaped cornea-like material (CLM), displaying the shape, curvature, thickness, and transparency of normal cornea. This polymerization of collagen appears to derive from some morphogenetic influence exerted by the corneo-scleral rim. Once the CLM had formed naturally, we used collagen crosslinking to fortify it, and then introduced cells to generate a stratified epithelial layer to create cornea-like tissue (CLT) displaying characteristics of native cornea. Through the excision and reuse of rims, each rim turned out to be useful for the generation of multiple cornea-shaped CLTs. CONCLUSIONS: The approach effectively helps to shorten the gap between demand and supply of CLMs/CLTs for transplantation. We are exploring the surgical transplantation of this CLT into animal eyes, as keratoprostheses, as a precursor to future applications involving human eyes. It is possible to use either the CLM or CLT, for patients with varying corneal blinding diseases.

Metal co-factors to enhance catalytic activity of short prion-derived peptide sequences.

Development of biomolecular enzyme mimics to efficiently catalyse biochemical reactions are of prime relevance for the bulk scale production of industrially relevant biocatalyst. In this regard, amyloidogenic peptides act as suitable self-assembling scaffolds, providing stable nanostructures with high surface area facilitating biocatalysis. Herein, we rationally design two positional amyloidogenic peptide isomers, "Fmoc-VYYAHH (1)" and "Fmoc-VHHAYY (2)" considering catalytic and metal binding affinity of histidine and tyrosine when placed in periphery vs. inner core of the peptide sequence. With an ultimate objective of designing metalloenzyme mimic, we choose Co2+ and Cu2+ as divalent transition metal cations for peptide complexation to aid in catalysis. After optimizing self-assembly of innate peptides, we investigate metal-peptide binding ratio and co-ordination, finally selecting 1:1 peptide metal complex suitable for biocatalysis. Metallopeptides act as better catalysts than the innate peptides as acyl esterase when tyrosines were present at the periphery. Kinetic parameters for assessing hydrolysis rate were calculated by fitting data into Michaelis-Menten and Lineweaver Burk plots. Catalytic activity is altered depending on the stability of peptide metal complexes. 2-Cu acting as the best biocatalyst with a kcat/KM = 0.08 M/s. The protocols mentioned in this chapter meticulously cover the design, synthesis, self-assembly and enzyme kinetics.

Photothermally switchable peptide nanostructures towards modulating catalytic hydrolase activity.

Enzymes are the most efficient catalysts in nature that possess an impressive range of catalytic activities, albeit limited by stability in adverse conditions. Functional peptides have emerged as alternative robust biocatalysts to mimic complex enzymes. Here, a rational design of minimalistic amyloid-inspired peptides 1-2 is demonstrated, which leads to pathway-driven self-assembly triggered by heat, light and chemical cues to render 1D and 2D nanostructures by the interplay of hydrogen bonding, host-guest interaction and reversible photodimerization. Such in situ transformable peptide nanostructures by means of external cues are envisaged as a catalytic amyloid for the first time to mimic the hydrolase enzyme activity. Michaelis Menten's enzyme kinetic parameters for the hydrolysis rate correlate the external cue-mediated structure-function augmentation with the twisted bundles, 1TB being the most efficient biocatalyst among all the dimensionally diverse nanostructures. Unlike the natural enzyme, the peptide nanostructures exhibited the robust nature of the hydrolase activity over a broad range of temperature and pH. Finally, the peptide nanostructures are explored as efficient heterogeneous flow catalysts to improve the turnover number for the hydrolase activity.