Minimalist De Novo Design of an Artificial Enzyme.

We employed a reductionist approach in designing the first heterochiral tripeptide that forms a robust heterogeneous short peptide catalyst similar to the "histidine brace" active site of lytic polysaccharide monooxygenases. The histidine brace is a conserved divalent copper ion-binding motif that comprises two histidine side chains and an amino group to create the T-shaped 3N geometry at the reaction center. The geometry parameters, including a large twist angle (73°) between the two imidazole rings of the model complex, are identical to those of native lytic polysaccharide monooxygenases (72.61°). The complex was synthesized and characterized as a structural and functional mimic of the histidine brace. UV-vis, vis-circular dichroism, Raman, and electron paramagnetic resonance spectroscopic analyses suggest a distorted square-pyramidal geometry with a 3N coordination at pH 7. Solution- and solid-state NMR results further confirm the 3N coordination in the copper center of the complex. The complex is pH-dependent and could catalyze the oxidation of benzyl alcohol in water to benzaldehyde with yields up to 82% in 3 h at pH 7 and above at 40 °C. The catalyst achieved 100% selectivity for benzaldehyde compared to conventional copper catalysis. The design of such a minimalist building block for functional soft materials with a pH switch can be a stepping stone in addressing needs for a cleaner and sustainable future catalyst.

Electric field modulated peptide based hydrogel nanocatalysts.

The ability to modulate self-assembly is the key to manufacture application-oriented materials. In this study, we investigated the effect of three independent variables that can modulate the catalytic activity of self-assembling peptides. The first two variables, amino acid sequence and its stereochemistry, were examined for their specific roles in the epitaxial growth and hydrogelation properties of a series of catalytic tripeptides. We observed that aromatic π-π interactions that direct the self-assembly of designed peptides, and the catalytic properties of hydrogels, are governed by the position and chirality of the proline residue. Subsequently, the influence of the third variable, an external electric field, was also tested to confirm its catalytic efficiency for the asymmetric C-C bond-forming aldol reaction. In particular, the electric field treated pff and PFF gels showed 10 and 36% higher stereoselectivity, respectively, compared with the control. Structure-property analysis using CD and FTIR spectroscopy indicates the electric field-induced beta to non-beta conformational transition in the peptide secondary structure, which corroborates with its reduced cross-link density and fibril width, respectively. Amplitude sweep rheology of the gels suggests a decrease in the storage modulus, with increased field strength. The results showed that an electric field of optimal strength can modulate the physical characteristics of the hydrogel, which in turn is manifested in the observed difference in enantioselectivity.

Topological effects on the designability and bactericidal potency of antimicrobial peptides.

New ideas and methods are being developed to generate highly designable small functional protein folds beyond the confines of natural structures, from secondary to quaternary level. Highly designable folds can have multiple sequence solutions, which are thermodynamically and kinetically stable. We have previously described how short syndiotactic helices can be exceptionally stable energetically, and how they can be used as a template for designing antibacterial agents. In this work, we have designed four syndiotactic, single turn, amphipathic; cationic 7-mer peptides which are the sequence and structural subset of earlier published 12-mer sequences. We examined the stability of the designed structures and its effects on the biological activity of such short peptide sequences. This was achieved by making objective comparisons between 12-mer and 7-mer sequences in terms of their antibacterial activity. Further, we investigated the mechanistic origins of clearly different bactericidal potency of single (7-mer) and double (12-mer) turn syndiotactic helices using molecular dynamics simulations. Our results suggest that conformationally constrained stable short double turn peptide scaffolds are highly designable, whereas single turn structures are more likely to be disordered. The stability of the designed peptide structure provides a platform for inclusion of multiple sequence variables and defined electrostatic fingerprints. Therefore, a stable peptide scaffold along with pre-defined electrostatic signatures can together be utilized for the design of novel antimicrobial peptides.

Electric Field Disruption of Amyloid Aggregation: Potential Noninvasive Therapy for Alzheimer's Disease.

The aggregation of ß-amyloid peptides is a key event in the formative stages of Alzheimer's disease. Promoting folding and inhibiting aggregation was reported as an effective strategy in reducing Aß-elicited toxicity. This study experimentally investigates the influence of the external electric field (EF) and magnetic field (MF) of varying strengths on the in vitro fibrillogenesis of hydrophobic core sequence, Aß16-22, and its parent peptide, Aß1-42. Biophysical methods such as ThT fluorescence, static light scattering, circular dichroism, and infrared spectroscopy suggest that EF has a stabilizing effect on the secondary structure, initiating a conformational switch of Aß16-22 and Aß1-42 from ß to non-ß conformation. This observation was further corroborated by dynamic light scattering and transmission electron microscopic studies. To mimic in vivo conditions, we repeated ThT fluorescence assay with Aß1-42 in human cerebrospinal fluid to verify EF-mediated modulation. The self-seeding of Aß1-42 and cross-seeding with Aß1-40 to verify that the autocatalytic amplification of self-assembly as a result of secondary nucleation also yields comparable results in EF-exposed and unexposed samples. Aß-elicited toxicity of EF-treated samples in two neuroblastoma cell lines (SH-SY5Y and IMR-32) and human embryonic kidney cell line (HEK293) were found to be 15-38% less toxic than the EF untreated ones under identical conditions. Experiments with fluorescent labeled Aß1-42 to correlate reduced cytotoxicity and cell internalization suggest a comparatively smaller uptake of the EF-treated peptides. Our results provide a scientific roadmap for future noninvasive, therapeutic solutions for the treatment of Alzheimer's disease.

Modulation of Peptide Based Nano-Assemblies with Electric and Magnetic Fields.

Peptide based nano-assemblies with their self-organizing ability has shown lot of promise due to their high degree of thermal and chemical stability, for biomaterial fabrication. Developing an effective way to control the organization of these structures is important for fabricating application-oriented materials at the molecular level. The present study reports the impact of electric and magnetic field-mediated perturbation of the self-assembly phenomenon, upon the chemical and structural properties of diphenylalanine assembly. Our studies show that, electric field effectively arrests aggregation and self-assembly formation, while the molecule is allowed to anneal in the presence of applied electric fields of varying magnitudes, both AC and DC. The electric field exposure also modulated the morphology of the self-assembled structures without affecting the overall chemical constitution of the material. Our results on the modulatory effect of the electric field are in good agreement with theoretical studies based on molecular dynamics reported earlier on amyloid forming molecular systems. Furthermore, we demonstrate that the self-assemblies formed post electric-field exposure, showed difference in their crystal habit. Modulation of nano-level architecture of peptide based model systems with external stimulus, points to a potentially rewarding strategy to re-work proven nano-materials to expand their application spectrum.