Temporal Self-Regulation of Mechanical Properties via Catalytic Amyloid Polymers of a Short Peptide.

We report a short peptide that accessed dynamic catalytic polymers to demonstrate four-stage (sol-gel-weak gel-strong gel) temporal self-regulation of its mechanical properties. The peptide exploited its intrinsic catalytic capabilities of manipulating C-C bonds (retro-aldolase-like) that resulted in a nonlinear variation in the catalytic rate. The seven-residue sequence exploited two lysines for binding and cleaving the thermodynamically activated substrate that subsequently led to the self-regulation of the mechanical strengths of the polymerized states as a function of time and reaction progress. Interestingly, the polymerization events were modulated by the different catalytic potentials of the two terminal lysines to cleave the substrate, covalently trap the electrophilic products, and subsequently control the mechanical properties of the system.

Dual enzyme-powered chemotactic cross ß amyloid based functional nanomotors.

Nanomotor chassis constructed from biological precursors and powered by biocatalytic transformations can offer important applications in the future, specifically in emergent biomedical techniques. Herein, cross ß amyloid peptide-based nanomotors (amylobots) were prepared from short amyloid peptides. Owing to their remarkable binding capabilities, these soft constructs are able to host dedicated enzymes to catalyze orthogonal substrates for motility and navigation. Urease helps in powering the self-diffusiophoretic motion, while cytochrome C helps in providing navigation control. Supported by the simulation model, the design principle demonstrates the utilization of two distinct transport behaviours for two different types of enzymes, firstly enhanced diffusivity of urease with increasing fuel (urea) concentration and secondly, chemotactic motility of cytochrome C towards its substrate (pyrogallol). Dual catalytic engines allow the amylobots to be utilized for enhanced catalysis in organic solvent and can thus complement the technological applications of enzymes.

Emergence of Catalytic Triad by Short Peptide Based Nanofibrillar Assemblies.

Through millions of years of the evolutionary journey, contemporary enzymes observed in extant metabolic pathways have evolved to become specialized, in contrast to their ancestors, which displayed promiscuous activities with wider substrate specificities. However, there remain critical gaps in our understanding of how these early enzymes could show such catalytic versatility despite lacking the complex three-dimensional folds of the existing modern-day enzymes. Herein, we report the emergence of a promiscuous catalytic triad by short amyloid peptide based nanofibers that access paracrystalline folds of ß-sheets to expose three residues (lysine, imidazole, and tyrosine) toward solvent. The ordered folded nanostructures could simultaneously catalyze two metabolically relevant chemical transformations via C-O and C-C bond manipulations, displaying both hydrolase and retro-aldolase-like activities. Further, the latent catalytic capabilities of the short peptide based promiscuous folds also helped in processing a cascade transformation, suggesting the important role they might have played in protometabolism and early evolutionary processes.

Fluorescent Microswimmers Based on Cross-ß Amyloid Nanotubes and Divergent Cascade Networks.

Shaped through millions of years of evolution, the spatial localization of multiple enzymes in living cells employs extensive cascade reactions to enable highly coordinated multimodal functions. Herein, by utilizing a complex divergent cascade, we exploit the catalytic potential as well as templating abilities of streamlined cross-ß amyloid nanotubes to yield two orthogonal roles simultaneously. The short peptide based paracrystalline nanotube surfaces demonstrated the generation of fluorescence signals within entangled networks loaded with alcohol dehydrogenase (ADH). The nanotubular morphologies were further used to generate cascade-driven microscopic motility through surface entrapment of sarcosine oxidase (SOX) and catalase (Cat). Moreover, a divergent cascade network was initiated by upstream catalysis of the substrate molecules through the surface mutation of catalytic moieties. Notably, the resultant downstream products led to the generation of motile fluorescent microswimmers by utilizing the two sets of orthogonal properties and, thus, mimicked the complex cascade-mediated functionalities of extant biology.

Substrate induced generation of transient self-assembled catalytic systems.

Living matter is sustained under non-equilibrium conditions via continuous expense of energy which is coordinated by complex organized events. Spatiotemporal control over exquisite functions arises from chemical complexity under non-equilibrium conditions. For instance, extant biology often uses substrate binding events to access temporally stable protein conformations which show acceleration of catalytic rates to subsequently degrade the substrate. Furthermore, thermodynamically activated but kinetically stable esters (GTP) induce the change of conformation of cytoskeleton proteins (microtubules) which leads to rapid polymerization and triggers an augmentation of catalytic rates to subsequently degrade the ester. Importantly, high-energy assemblies composed of non-activated building blocks (GDP-tubulin) are accessed utilizing the energy dissipated from the catalytic conversion of GTP to GDP from the assembled state. Notably, some experimental studies with simple self-assembled systems have elegantly mimicked the phenomena of substrate induced transient generation of catalytic conformations. Through this review, we endeavour to highlight those select studies which have used simple building blocks to demonstrate substrate induced self-assemblies that subsequently show rate acceleration to convert the substrate into waste. The concept of substrate induced self-assembly of building blocks and rate acceleration from the assembled state has the potential to play a predominant role in the preparation of non-equilibrium systems. The design strategies covered in this review can inspire the possibilities of accessing high energy self-assembled structures that are seen in living systems.

Non-Equilibrium Polymerization of Cross-ß Amyloid Peptides for Temporal Control of Electronic Properties.

Hydrophobic collapse plays crucial roles in protein functions, from accessing the complex three-dimensional structures of native enzymes to the dynamic polymerization of non-equilibrium microtubules. However, hydrophobic collapse can also lead to the thermodynamically downhill aggregation of aberrant proteins, which has interestingly led to the development of a unique class of soft nanomaterials. There remain critical gaps in the understanding of the mechanisms of how hydrophobic collapse can regulate such aggregation. Demonstrated herein is a methodology for non-equilibrium amyloid polymerization through mutations of the core sequence of Aß peptides by a thermodynamically activated moiety. An out of equilibrium state is realized because of the negative feedback from the transiently formed cross-ß amyloid networks. Such non-equilibrium amyloid nanostructures were utilized to access temporal control over its electronic properties.