Sequence adaptive peptide-polysaccharide nanostructures by biocatalytic self-assembly

Coassembly of peptides and polysaccharides can give rise to the formation of nanostructures with tunable morphologies. We show that in situ enzymatic exchange of a dipeptide sequence in aromatic peptide amphiphiles/polysaccharide coassemblies enables dynamic formation and degradation of different nanostructures depending on the nature of the polysaccharide present. This is achieved in a one-pot system composed of Fmoc-cysteic acid (CA) and Fmoc-lysine (K) plus phenylalanine amide (F) in the presence of thermolysin that, through dynamic hydrolysis and amide formation, gives rise to a dynamic peptide library composed of the corresponding Fmoc-dipeptides (CAF and KF). When the cationic polysaccharide chitosan is added to this mixture, selective amplification of the CAF peptide is observed giving rise to formation of nanosheets through coassembly. By contrast, upon addition of anionic heparin, KF is formed that gives rise to a nanotube morphology. The dynamic adaptive potential was demonstrated by sequential morphology changes depending on the sequence of polysaccharide addition. This first demonstration of the ability to access different peptide sequences and nanostructures, depending on the presence of biopolymers, may pave the way to biomaterials that can adapt their structure and function and may be of relevance in the design of materials able to undergo dynamic morphogenesis

Emergence of function and selection from recursively programmed polymerisation reactions in mineral environments

Living systems are characterised by an ability to sustain chemical reaction networks far‐from‐equilibrium. It is likely that life first arose through a process of continual disruption of equilibrium states in recursive reaction networks, driven by periodic environmental changes allowing the emergence of a memory. Herein, we report the emergence of proto‐enzymatic function from recursive polymerisation reactions using amino acids and glycolic acid over four wet‐dry cycles. Reactions are kept out of equilibrium by diluting products 9:1 in fresh starting solution at the end of each recursive cycle, and the development of complex high molecular weight species is explored using a new metric, the Mass Index, which allows the complexity of the system to be explored as a function of cycle. This process is carried out on a range of different mineral environments. We explore the hypothesis that disrupting equilibrium via recursive cycling imposes a selection pressure and subsequent boundary conditions on products, which may otherwise be prone to uncontrolled combinatorial explosion. After just four reaction cycles, product mixtures from recursive reactions exhibit greater catalytic activity and truncation of product space towards higher molecular weight species compared to non‐recursive controls

Biocatalytic self-assembly on magnetic nanoparticles

Combining (bio-)catalysis and molecular self-assembly provides an effective approach for the production and processing of self-assembled materials, by exploiting catalysis to direct the assembly kinetics and hence control the formation of ordered nanostructures. Applications of (bio-)catalytic self-assembly in biologically interfacing systems and in nanofabrication have recently been reported. Inspired by self-assembly in biological cells, efforts to confine catalysts on flat or patterned surfaces to exert spatial control over molecular gelator generation and nanostructure self-assembly have also emerged. Building on our previous work in the area, we demonstrate in this report the use of enzymes immobilized onto magnetic nanoparticles (NPs) to spatially localize the initiation of peptide self-assembly into nanofibers around NPs. The concept is generalized for both an equilibrium biocatalytic system that forms stable hydrogels and a non-equilibrium system that normally has a preset lifetime. Characterization of the hydrogels shows that self-assembly occurs at the site of enzyme immobilization on the NPs, to give rise to gels with a “hub-and-spoke” morphology where the nanofibers are linked through the enzyme-NP conjugates. This NP-controlled arrangement of self-assembled nanofibers enables remarkable enhancements in the shear strength of both hydrogel systems, as well as a dramatic extension of the hydrogel stability in the non-equilibrium system. We are also able to show that the use of magnetic NPs enables external control of both the formation of the hydrogel and its overall structure by application of an external magnetic field. We anticipate that the enhanced properties and stimuli-responsiveness of our NP-enzyme system will have applications ranging from nanomaterial fabrication to biomaterials and biosensing

Integrated synthesis of nucleotide and nucleosides influenced by amino acids

Research on prebiotic chemistry and the origins of nucleic acids and proteins has traditionally been focussed on only one or the other. However, if nucleotides and amino acids co-existed on the early Earth, their mutual interactions and reactivity should be considered explicitly. Here we set out to investigate nucleotide/nucleoside formation by simple dehydration reactions of constituent building blocks (sugar, phosphate, and nucleobase) in the presence of different amino acids. We demonstrate the simultaneous formation of glycosidic bonds between ribose, purines, and pyrimidines under mild conditions without catalysts or activated reagents, as well as nucleobase exchange, in addition to the simultaneous formation of nucleotide and nucleoside isomers from several nucleobases. Clear differences in the distribution of glycosylation products are observed when glycine is present. This work demonstrates that reaction networks of nucleotides and amino acids should be considered when exploring the emergence of catalytic networks in the context of molecular evolution

Alignment of nanostructured tripeptide gels by directional ultrasonication

We demonstrate an in-situ ultrasonic approach to influence self-assembly across the supramolecular to micron length scales, showing enhancement of supramolecular interactions, chirality and orientation, which depends on the peptide sequence and solvent environment. This is the first successful demonstration of using oscillating pressure waves to generate anisotropic organo- and hydro- gels consisting of oriented tripeptides structures

Environmental control programs the emergence of distinct functional ensembles from unconstrained chemical reactions

Many approaches to the origin of life focus on how the molecules found in biology might be made in the absence of biological processes, from the simplest plausible starting materials. Another approach could be to view the emergence of the chemistry of biology as process whereby the environment effectively directs “primordial soups” toward structure, function, and genetic systems over time. This does not require the molecules found in biology today to be made initially, and leads to the hypothesis that environment can direct chemical soups toward order, and eventually living systems. Herein, we show how unconstrained condensation reactions can be steered by changes in the reaction environment, such as order of reactant addition, and addition of salts or minerals. Using omics techniques to survey the resulting chemical ensembles we demonstrate there are distinct, significant, and reproducible differences between the product mixtures. Furthermore, we observe that these differences in composition have consequences, manifested in clearly different structural and functional properties. We demonstrate that simple variations in environmental parameters lead to differentiation of distinct chemical ensembles from both amino acid mixtures and a primordial soup model. We show that the synthetic complexity emerging from such unconstrained reactions is not as intractable as often suggested, when viewed through a chemically agnostic lens. An open approach to complexity can generate compositional, structural, and functional diversity from fixed sets of simple starting materials, suggesting that differentiation of chemical ensembles can occur in the wider environment without the need for biological machinery

Mechanistic insights into phosphatase triggered self-assembly including enhancement of biocatalytic conversion rate

We report on the mechanistic investigation of alkaline phosphatase (AP) triggered self-assembly and hydrogelation of Fmoc-tyrosine (Fmoc-Y). We studied separately the biocatalytic conversion using HPLC, changes in supramolecular interactions and chirality using CD and fluorescence spectroscopy, nanostructure formation by AFM and gelation by oscillatory rheometry. Three consecutive stages could be distinguished (which may overlap, depending on the enzyme concentration). Typically, the phosphorylated Fmoc-Y (Fmoc-pY) undergoes rapid and complete dephosphorylation, followed by formation of aggregates which reorganise into nanofibres and consequently give rise to gelation. We observed a remarkable enhancement of catalytic activity during the early stages of the self-assembly process, providing evidence for enhancement of enzymatic activation by the supramolecular structures formed. Overall, this study provides a further step in understanding biocatalytic self-assembly

Versatile pectin grafted poly (N-isopropylacrylamide); modulated targeted drug release

This study describes synthesis and optimization of pectin grafted poly(N-isopropylacrylamide) hydrogels as vehicles for colon-targeted theophylline model drug release. The gels were prepared in the presence of N, N′–methylenebisacrylamide (MBAA) crosslinker and ceric ammonium nitrate (CAN) initiator under N2 atmosphere. Optimum conditions, in terms of percent of grafting (%G), were determined as follows: pectin = 1.0 g, [NIPAAm] = 26.51 mM, [MBAA] = 0.65 mM, [CAN] = 0.073 mM, polymerization temperature = 30°C and time = 4.0 h. Hydrogels were characterized by FTIR, TGA, DSC, XRD and SEM. The formed hydrogel did not have a thermo-sensitivity behavior. The in vitro percent drug release was studied in terms of different percent of grafting and different polymerization temperatures under two pH values namely 5.5 and 7.4. Conclusively, the optimum colon-targeted vehicle properties that provide the least drug release at pH5.5 and the most drug release at pH7.4 were as follows: [NIPAAm] = 26.51 mM and [MBAA] = 0.56 mM, polymerization temperature = 30°C and %G = 55.5

Enzyme-responsive hydrogels for biomedical applications

This chapter highlights recent developments in enzyme-responsive gels. The focus is on peptide-based small-molecule hydrogels, for biomedical applications. The use of enzymes in this context provides a powerful methodology for controlled assembly, taking advantage of both biological selectivity and catalytic amplification. The building blocks for self-assembly and basic design rules for small molecule peptide gelators are discussed first. This is followed by a discussion of key features of biocatalytic self-assembly of hydrogels, focusing on control of nanoscale organization and consequent function. Finally, the potential applications of the enzyme-responsive hydrogels as biomaterials are discussed in the areas of cell culture, drug delivery, biosensing, and control of cell fate