Abstract
Self-assembling peptides are attracting wide interest as biodegradable building blocks to achieve functional nanomaterials that do not persist in the environment. Amongst the many applications, biocatalysis is gaining momentum, although a clear structure-to-activity relationship is still lacking. This work applied emerging design rules to the heterochiral octapeptide sequence His–Leu–DLeu–Ile–His–Leu–DLeu–Ile for self-assembly into nanofibrils that, at higher concentration, give rise to a supramolecular hydrogel for the mimicry of esterase-like activity. The peptide was synthesized by solid-phase and purified by HPLC, while its identity was confirmed by 1H-NMR and electrospray ionization (ESI)-MS. The hydrogel formed by this peptide was studied with oscillatory rheometry, and the supramolecular behavior of the peptide was investigated with transmission electron microscopy (TEM) analysis, circular dichroism (CD) spectroscopy, thioflavin T amyloid fluorescence assay, and attenuated total reflectance (ATR) Fourier-transform infrared (FT-IR) spectroscopy. The biocatalytic activity was studied by monitoring the hydrolysis of p-nitrophenyl acetate (pNPA) at neutral pH, and the reaction kinetics followed an apparent Michaelis–Menten model, for which a Lineweaver–Burk plot was produced to determine its enzymatic parameters for a comparison with the literature. Finally, LC–MS analysis was conducted on a series of experiments to evaluate the extent of, if any, undesired peptide acetylation at the N-terminus. In conclusion, we provide new insights that allow gaining a clearer picture of self-assembling peptide design rules for biocatalysis.
Highlights
Enzymes have long been a great source of inspiration for organic chemists to develop new catalysts for industrial applications, as well as to achieve simple, low-cost mimetics that display activity in water and that are biodegradable, so that they do not persist in the environment [1]
One of the simplest approaches consists of the use of short peptides, since it is possible to directly incorporate the specific residues that perform the enzymatic catalysis in the amino-acid sequence
Hydrolases are a class of enzymes that are of high relevance for industrial applications and for organic synthesis; they provide a good target for biomimicry
Summary
Enzymes have long been a great source of inspiration for organic chemists to develop new catalysts for industrial applications, as well as to achieve simple, low-cost mimetics that display activity in water and that are biodegradable, so that they do not persist in the environment [1]. Amongst the various approaches to achieve a self-assembling short peptide, an attractive strategy features the inclusion of both D- and L-amino acids at specific positions along a heterochiral sequence, whereby nanostructured hydrogels can be formed even with just three amino acids, while their homochiral isomers typically precipitate in water [18]. These supramolecular systems feature amphipathic assemblies, whereby the different stereoconfiguration allows displaying hydrophobic side chains on the same side of the peptide backbone [19,20]. The choice for an octapeptide allows for a more appropriate comparison with other biocatalysts that feature two His residues and a similar number of amino acids [13,15,22]
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