Herein, we report a conjugation strategy, where we utilize a poly­(ethylene oxide) cylindrical molecular brush architecture to design a self-assembled structure for thermal stabilization of enzymes. We demonstrate that the proposed architecture of the moderately stiff polymer ligand results in a significant improvement of biocatalytic activity and thermal stability of lysozyme and trypsin that retain their activity, even upon heating to 100 °C and above. The molecular brush is bound via epoxy functional groups to the amino groups of the lysine on the surface of the enzyme globule, promoting the formation of stiff and crowded cages around the enzymes and preventing the water molecules access to the enzyme and enzymes agglomeration. The molecular dynamic simulations show that the high concentration of poly­(ethylene oxide) in the vicinity of the enzyme is critical for their stability. Monitoring of lysozyme–molecular brush conjugates for 6 and 12 months in lyophilized form and in solution, respectively, has shown that the conjugation does not compromise the shelf life of the enzyme.

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We fabricated thermoplastic surfaces possessing extremely limited water and oil wettability without employment of long-chain perfluoroalkyl (LCPFA) substances. Namely, by taking advantage of the structure and behavior of original oleophobic perfluoropolyether (PFPE) methacrylate (PFM) molecular bottlebrush (MBB) additive we obtained polymeric surfaces with oil contact angles well above 80° and surface energy on the level of 10 mN/m. Those angles and surface energies are the highest and the lowest respective values reported to date for any bulk solid flat organic surface not containing LCPFA. We show experimentally and computationally that this remarkable oil repellency is attributed to migration of small quantities of the oleophobic MBB additives to the surface of the thermoplastics. Severe mismatch in the affinity between the densely grafted long side chains of MBB and a host matrix promotes stretching and densification of mobile side chains delivering the lowest surface energy functionalities (CF3) to the materials’ boundary. Our studies demonstrate that PFM can be utilized as an effective low surface energy additive to conventional thermoplastic polymers, such as poly­(methyl methacrylate) and Nylon-6. We show that films containing PFM achieve the level of oil repellency significantly higher than that of polytetrafluoroethylene (PTFE), a fully perfluorinated thermoplastic. The surface energy of the films is also significantly lower than that of PTFE, even at low concentrations of PFM additives.

Designing biomaterials capable of functioning in harsh environments is vital for a range of applications. Using molecular dynamics simulations, we show that conjugating lysozymes with a copolymer [poly(GMA- stat-OEGMA)] comprising glycidyl methacrylate (GMA) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) results in a dramatic increase of stability of these enzymes at high temperatures provided that the concentration of the copolymer in the close vicinity of the enzyme exceeds a critical value. In our simulations, we use triads containing the same ratio of GMA to OEGMA units as in our recent experiments (N. S. Yadavalli et al., ACS Catalysis, 2017, 7, 8675). We focus on the dynamics of the conjugate at high temperatures and on its structural stability as a function of the copolymer/water content in the vicinity of the enzyme. We show that the dynamics of phase separation in the water-copolymer mixture surrounding the enzyme is critical for the structural stability of the enzyme. Specifically, restricting water access promotes the structural stability of the lysozyme at high temperatures. We identified critical water concentration below which we observe a robust stabilization; the phase separation is no longer observed at this low fraction of water so that the water domains promoting unfolding are no longer formed in the vicinity of the enzyme. This understanding provides a basis for future studies on designing a range of enzyme-copolymer conjugates with improved stability.

Protein stability and performance in various natural and artificial systems incorporating many other macromolecules for therapeutic, diagnostic, sensor, and biotechnological applications attract increasing interest with the expansion of these technologies.Here we address the catalytic activity of lysozyme protein (LYZ) in the presence of a polyethylene glycol (PEG) crowder in a broad range of concentrations and temperatures in aqueous solutions of two different molecular mass PEG samples (M w = 3350 and 10000 g/mol). The phase behavior of PEG−protein solutions is examined by using dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS), while the enzyme denaturing is monitored by using an activity assay (AS) and circular dichroism (CD) spectroscopy. Molecular dynamic (MD) simulations are used to illustrate the effect of PEG concentration on protein stability at high temperatures. The results demonstrate that LYZ residual activity after 1 h incubation at 80 °C is improved from 15% up to 55% with the addition of PEG. The improvement is attributed to two underlying mechanisms. (i) Primarily, the stabilizing effect is due to the suppression of the enzyme aggregation because of the stronger PEG−protein interactions caused by the increased hydrophobicity of PEG and lysozyme at elevated temperatures. (ii) The MD simulations showed that the addition of PEG to some degree stabilizes the secondary structures of the enzyme by delaying unfolding at elevated temperatures. The more pronounced effect is observed with an increase in PEG concentration. This trend is consistent with CD and AS experimental results, where the thermal stability is strengthened with increasing of PEG concentration and molecular mass. The results show that the highest stabilizing effect is approached at the critical overlap concentration of PEG.

The abnormal aggregation of amyloid proteins is reported to play a critical role in the etiology of neurodegenerative disorders. Studies have shown that excessive ferric irons are associated with the misfolding of amyloid proteins, and that (-)-epigallocatechin gallate (EGCG) is a good metallic ion chelator with inhibitory effect on the aggregation of amyloid proteins. EGCG has been thus considered as a potential drug candidate for the treatment of neurodegenerative diseases. However, the mechanism of action for EGCG in inhibition of aggregation of amyloid proteins is still remaining unclear. Silk fibroin (SF) shares similarities with amyloid proteins in some amino acid sequences and fibrillation kinetics. In this work, therefore, we used SF as a model of protein to investigate the effects of Fe(III) and EGCG on conformational transition by using turbidity assay, thioflavin T (ThT) fluorescence spectroscopy, Raman spectroscopy, and atomic force microscope (AFM). We demonstrated that low concentration of Fe(III) ions promoted the formation of β-sheet conformers, while high concentration of Fe(III) ions inhibited further aggregation of SF. EGCG could significantly inhibit the conformational transition of SF when induced by Fe(III), and decrease the amount of β-sheet conformers dose-dependently. The findings provide important information regarding to EGCG as a potential agent for the prevention and treatment of neurodegenerative diseases. Fe(III) can accelerate the conformation transition of silk fibrion (SF) from random coil into β-sheet, while (-)-epigallocatechin gallate (EGCG) inhibits Fe(III)-induced β-sheet aggregation of SF., 2016. © 2015 Wiley Periodicals, Inc. Biopolymers 105: 100-107, 2016.

In order to overcome the drawbacks of silk fibroin (SF)-based materials, SF has been blended with some polymers. Before using the blend material, understanding of the structures and phase behaviors of the blend is thought to be essential. In this study, solid-state (13)C CP-MAS NMR and Raman imaging techniques were used to study the structures and phase behaviors of blends of SF with polyethylene glycol (PEG) at a molecular weight that varied from 2 to 20 kDa and a blend ratio of SF/PEG from 95/5 to 70/30 (w/w%) at the molecular and microscopic levels. It is found that the conformational transition of SF to the β-sheet increased as the PEG content increased, while the amount of the formed β-sheet conformers was decreased as the PEG molecular weight increased for a given content. It is also observed that SF was incompatible with PEG to some extent. The phase separation into "sea" and "island" domains took place in the SF/PEG blend films. SF was dominantly present in the "sea" domain, while PEG in the "island" domains. The conformation of SF in the interface between SF and PEG was changed to the β-sheet, while that in the protein-rich domain remained in the random coil and/or helix conformation. These observations suggest that the specifically expected materials, for example, the silk-based microspheres or scaffold materials can be manufactured by controlling the molecular weight and content of PEG in the blend system.

Using dissipative particle dynamics, we characterize dynamics of aggregation of molecular bottlebrushes in solvents of various qualities by tracking the number of clusters, the size of the largest cluster, and an average aggregation number. We focus on a low volume fraction of bottlebrushes in a range of solvents and probe three different cutoff criteria to identify bottlebrushes belonging to the same cluster. We demonstrate that the cutoff criteria which depend on both the coordination number and the length of the side chain allows one to correlate the agglomeration status with the structural characteristics of bottlebrushes in solvents of various qualities. We characterize conformational changes of the bottlebrush within the agglomerates with respect to those of an isolated bottlebrush in the same solvents. The characterization of bottlebrush conformations within the agglomerates is an important step in understanding the relationship between the bottlebrush architecture and material properties. An analysis of three distinct cutoff criteria to identify bottlebrushes belonging to the same cluster introduces a framework to identify both short-lived transient and long-lived agglomerates; the same approach could be further extended to characterize agglomerates of various macromolecules with complex architectures beyond the specific bottlebrush architecture considered herein.