Enzyme‐Mimicking Peptides to Catalytically Grow ZnO Nanocrystals in Non‐Aqueous Environments

Abstract

The application of enzymesf or biomimetic material growth is ap otential path to breakthroughs in catalytic inorganic nanocrystal synthesis because the biocatalytic functions of proteins can lead to highly efficient growth of materials with accurate structures at low temperature. However,m any metal nanocrystals are grown in organic solvents, which is not an ideal environment for biomineralization with enzymes due to denaturing of catalytic pocket structures. Here, we applied ac atalytic CP4 peptide, optimized for protease reactions such as amide and ester hydrolysis, to test the catalytic ZnO nanocrystal growth in non-aqueous environments and the performance was compared with the enzyme subtilisin. We demonstrated that the CP4 catalytic peptide, evolved by the hydrogel-based combinatory phage display library, could grow ZnO nanoparticles from zinc acetate precursors in higher crystallinitya nd yield, as compared to the protease enzyme, in an organics olvent by catalyzing ester-elimination of precursors at room temperature.T his result indicates that catalytic oligopeptides, which possess no rigid 3D structures but are rather flexible, could fold into the catalytically active conformation more frequently in harsh environments such as organic solvents.Complex biomolecular systemss uch as enzymes, viruses, and bacteria have been applied for inorganic nanocrystal synthesis. [1] While these systems could catalyze nanocrystal growth under ambient conditions in aqueous environments, for further diversecatalytic applications it is desirable to optimizetheir activities for tolerating harsh organic environments. Recently, peptides, short building blocks of proteins,h ave shown potential to possesst he catalytic activity for enzymatic reactions in materialg rowth. [2] While some peptides have been shown to exhibit high catalytic activity in chemical reactions and material growth in ambient conditions, [2g] these peptides are not directly discovered to catalyze the target material growth, but they are rather selected on the basis of binding affinity to intermediates and products.F or such direct screening of the binding event the phage displayl ibrary has been used extensively; however the direct discovery of catalytic peptides from ac ombinatory phage display library meets difficultyi nt he panning process;e ven though certain peptides from random sequences on phage viruses catalyze target reactions, the isolation of these catalytic peptides for the identification of sequences through gene analysisi sv ery difficult. Previously,p eptidec atalysts for the room temperature growth of inorganic materials were screened with ac ombinatory phage display library by directly mixingthe library system in precursor solutions, however it is necessary to choose precursors that do not grow anyb yproducts except target materials, and such as pecial condition is not generally applicable to screen peptides for av arietyo f chemicalr eactions. [3] Recently,anew strategy to discover peptide catalysts for various material syntheses was demo...

Design of Catalytic Peptides and Proteins Through Rational and Combinatorial Approaches

“…By contrast, flexible catalytic oligopeptides with no rigid 3D structures could maintain catalytic activities in such harsh environments. To test this hypothesis, investigators examined the catalytic ability of CP4 peptide (Figure 3c) to crystallize an oxide semiconductor material (82). Ester elimination(83) can synthesize various nanocrystalline materials, such as ZnO (83–85), CoO (86), CuO (87), Fe 3 O 4 /Fe 2 O 3 , and CoFe 2 O 4 (88).…”

“…To achieve this goal, we tested the ability of CP4 peptide to promote ZnO formation in methanol. Zinc acetate precursor dissolved in methanol was mixed with CP4 peptide (Figures 3c and 4a) (82). After incubation for 3 days at room temperature, flake-shaped ZnO formed (Figure 4b).…”

Biomimetic Crystallization of MnFe2O4 Mediated by Peptide‐Catalyzed Esterification at Low Temperature

“…Recently, protease-mimicking CP4 peptides were used to catalyze ZnO nanocrystal formation through ester elimination. [5] Ester elimination favors the growth of metal oxides from metal acetate precursors through reverse hydrolysis of esters in organic environments, such as alcohols at high temperature. [6] The CP4 peptide was discovered from a combinatorial phage-display peptide library through a hydrogel-based biopanning process where phage viruses possessing protease-like activity can be purified by centrifugation due to product gel formation around peptides displayed at the tail of viruses.…”

“…[6] The CP4 peptide was discovered from a combinatorial phage-display peptide library through a hydrogel-based biopanning process where phage viruses possessing protease-like activity can be purified by centrifugation due to product gel formation around peptides displayed at the tail of viruses. [5,7] Previously, this type of phage biopanning was also applied to identify peptides that can target cancer and stem cells. [8] The CP4 peptide is an efficient catalyst for metal oxide formation through the ester elimination pathway, and its amino acid residues (in particular, serine and lysine residues) could play an important role for crystallization.…”

“…[8] The CP4 peptide is an efficient catalyst for metal oxide formation through the ester elimination pathway, and its amino acid residues (in particular, serine and lysine residues) could play an important role for crystallization. [5] While protease can catalyze the reverse hydrolysis of ester, [9] natural proteases are not ideal catalysts for metallization reactions because of the use of organic solvents. Small-peptide catalysts could have an advantage in catalyzing ZnO formation through ester elimination in organic solvents because organic-solvent-induced denaturing could be less problematic, as the conformation of the catalytic pocket of enzymes is more sensitive to the environment.…”