Bionanocomposites with Enhanced Physical Properties from Curli Amyloid Assemblies and Cellulose Nanofibrils.

Proteinaceous amyloid fibrils are one of the stiffest biopolymers due to their extensive cross-ß-sheet quaternary structure, whereas cellulose nanofibrils (CNFs) exhibit interesting properties associated with their nanoscale size, morphology, large surface area, and biodegradability. Herein, CNFs were supplemented with amyloid fibrils assembled from the Curli-specific gene A (CsgA) protein, the main component of bacterial biofilms. The resulting composites showed superior mechanical properties, up to a 7-fold increase compared to unmodified CNF films. Wettability and thermogravimetric analyses demonstrated high surface hydrophobicity and robust thermal tolerance. Bulk spectroscopic characterization of CNF-CsgA films revealed key insights into the molecular organization within the bionanocomposites. Atomic force microscopy and photoinduced force microscopy revealed the high-resolution location of curli assemblies into the CNF films. This novel sustainable and cost-effective CNF-based bionanocomposites supplemented with intertwined bacterial amyloid fibrils opens novel directions for environmentally friendly applications demanding high mechanical, water-repelling properties, and thermal resistance.

Adsorption of Tannic Acid onto Gold Surfaces.

Thin film coatings are widely applicable in materials for consumer products, electronics, optical coatings, and even biomedical applications. Wet coating can be an effective method to obtain thin films of functional materials, and this technique has recently been studied in depth for the formation of bioinspired polyphenolic films. Naturally occurring polyphenols such as tannic acid (TA) have garnered interest due to their roles in biological processes and their applicability as antioxidants, antibacterial agents, and corrosion inhibitors. Understanding the adsorption of polyphenols to surfaces is a core aspect in the fabrication processes of thin films of these materials. In this work, the adsorption of TA to gold surfaces is measured using a quartz crystal microbalance with dissipation monitoring (QCMD) and surface plasmon resonance (SPR) for a wide range of TA concentrations. The adsorption kinetics, aggregation, and stability of TA solutions in physiological-like conditions are studied. Unexpectedly, it is found that the adsorption rates depend only weakly on concentration because of the presence of TA aggregates that do not adsorb. The mechanism of layer formation is also investigated, finding that TA monolayers readily adsorb onto gold with flat or edge-on molecular orientations dependent on the solution concentration. A mix of orientations in the intermediate case leads to slow multilayer adsorption.

Interactions of Polyphenolic Gallotannins with Amyloidogenic Polypeptides Associated with Alzheimer's Disease: From Molecular Insights to Physiological Significance.

Polyphenols are natural compounds abundantly found in plants. They are known for their numerous benefits to human health, including antioxidant properties and anti-inflammatory activities. Interestingly, many studies have revealed that polyphenols can also modulate the formation of amyloid fibrils associated with disease states and can prevent the formation of cytotoxic oligomer species. In this review, we underline the numerous effects of four hydrolysable gallotannins (HGTs) with high conformational flexibility, low toxicity, and multi-targeticity, e.g., tannic acid, pentagalloyl glucose, corilagin, and 1,3,6-tri-O-galloyl-ß-D-glucose, on the aggregation of amyloidogenic proteins associated with the Alzheimer's Disease (AD). These HGTs have demonstrated interesting abilities to reduce, at different levels, the formation of amyloid fibrils involved in AD, including those assembled from the amyloid ß-peptide, the tubulin-associated unit, and the islet amyloid polypeptide. HGTs were also shown to disassemble pre-formed fibrils and to diminish cognitive decline in mice. Finally, this manuscript highlights the importance of further investigating these naturally occurring HGTs as promising scaffolds to design molecules that can interfere with the formation of proteotoxic oligomers and aggregates associated with AD pathogenesis.

Contribution of the 12-17 hydrophobic region of islet amyloid polypeptide in self-assembly and cytotoxicity.

The islet amyloid polypeptide (IAPP) is a 37-residue aggregation-prone peptide hormone whose deposition as insoluble fibrils in the islets of Langerhans is associated with type II diabetes. Therapeutic interventions targeting IAPP amyloidogenesis, which contributes to pancreatic ß-cell degeneration, remain elusive owing to the lack of understanding of the self-assembly mechanisms and of the quaternary proteospecies mediating toxicity. While countless studies have investigated the contributions of the 20-29 amyloidogenic core in self-assembly, IAPP central region, i.e. positions 11 to 19, has been less studied, notwithstanding its potential key role in oligomerization. In this context, the present study aimed at investigating the physicochemical and conformational properties driving IAPP self-assembly and associated cytotoxicity. Computational tools and all-atom molecular dynamics simulation suggested that the hydrophobic 12-17 segment promotes IAPP self-recognition and aggregation. Alanine scanning revealed that the hydrophobic side chains of Leu12, Phe15 and Val17 are critical for amyloid fibril formation. Destabilization of the α-helical folding by Pro substitution enhanced self-assembly when the pyrrolidine ring was successively introduced at positions Ala13, Asn14 and Phe15, in comparison to respective Ala-substituted counterparts. Modulating the peptide backbone flexibility at position Leu16 through successive incorporation of Pro, Gly and α-methylalanine, inhibited amyloid formation and reduced cytotoxicity, while the isobutyl side chain of Leu16 was not critical for self-assembly and IAPP-mediated toxicity. These results highlight the importance of the 12-17 hydrophobic region of IAPP for self-recognition, ultimately supporting the development of therapeutic approaches to prevent oligomerization and/or fibrillization.

Molecular Interactions of Tannic Acid with Proteins Associated with SARS-CoV-2 Infectivity.

The overall impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on our society is unprecedented. The identification of small natural ligands that could prevent the entry and/or replication of the coronavirus remains a pertinent approach to fight the coronavirus disease (COVID-19) pandemic. Previously, we showed that the phenolic compounds corilagin and 1,3,6-tri-O-galloyl-ß-D-glucose (TGG) inhibit the interaction between the SARS-CoV-2 spike protein receptor binding domain (RBD) and angiotensin-converting enzyme 2 (ACE2), the SARS-CoV-2 target receptor on the cell membrane of the host organism. Building on these promising results, we now assess the effects of these phenolic ligands on two other crucial targets involved in SARS-CoV-2 cell entry and replication, respectively: transmembrane protease serine 2 (TMPRSS2) and 3-chymotrypsin like protease (3CLpro) inhibitors. Since corilagin, TGG, and tannic acid (TA) share many physicochemical and structural properties, we investigate the binding of TA to these targets. In this work, a combination of experimental methods (biochemical inhibition assays, surface plasmon resonance, and quartz crystal microbalance with dissipation monitoring) confirms the potential role of TA in the prevention of SARS-CoV-2 infectivity through the inhibition of extracellular RBD/ACE2 interactions and TMPRSS2 and 3CLpro activity. Moreover, molecular docking prediction followed by dynamic simulation and molecular mechanics Poisson-Boltzmann surface area (MMPBSA) free energy calculation also shows that TA binds to RBD, TMPRSS2, and 3CLpro with higher affinities than TGG and corilagin. Overall, these results suggest that naturally occurring TA is a promising candidate to prevent and inhibit the infectivity of SARS-CoV-2.

Corilagin and 1,3,6-Tri-O-galloy-ß-D-glucose: potential inhibitors of SARS-CoV-2 variants.

The COVID-19 disease caused by the virus SARS-CoV-2, first detected in December 2019, is still emerging through virus mutations. Although almost under control in some countries due to effective vaccines that are mitigating the worldwide pandemic, the urgency to develop additional vaccines and therapeutic treatments is imperative. In this work, the natural polyphenols corilagin and 1,3,6-tri-O-galloy-ß-d-glucose (TGG) are investigated to determine the structural basis of inhibitor interactions as potential candidates to inhibit SARS-CoV-2 viral entry into target cells. First, the therapeutic potential of the ligands are assessed on the ACE2/wild-type RBD. We first use molecular docking followed by molecular dynamics, to take into account the conformational flexibility that plays a significant role in ligand binding and that cannot be captured using only docking, and then analyze more precisely the affinity of these ligands using MMPBSA binding free energy. We show that both ligands bind to the ACE2/wild-type RBD interface with good affinities which might prevent the ACE2/RBD association. Second, we confirm the potency of these ligands to block the ACE2/RBD association using a combination of surface plasmon resonance and biochemical inhibition assays. These experiments confirm that TGG and, to a lesser extent, corilagin, inhibit the binding of RBD to ACE2. Both experiments and simulations show that the ligands interact preferentially with RBD, while weak binding is observed with ACE2, hence, avoiding potential physiological side-effects induced by the inhibition of ACE2. In addition to the wild-type RBD, we also study numerically three RBD mutations (E484K, N501Y and E484K/N501Y) found in the main SARS-CoV-2 variants of concerns. We find that corilagin could be as effective for RBD/E484K but less effective for the RBD/N501Y and RBD/E484K-N501Y mutants, while TGG strongly binds at relevant locations to all three mutants, demonstrating the significant interest of these molecules as potential inhibitors for variants of SARS-CoV-2.

Polyphenol-Peptide Interactions in Mitigation of Alzheimer's Disease: Role of Biosurface-Induced Aggregation.

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder, responsible for nearly two-thirds of all dementia cases. In this review, we report the potential AD treatment strategies focusing on natural polyphenol molecules (green chemistry) and more specifically on the inhibition of polyphenol-induced amyloid aggregation/disaggregation pathways: in bulk and on biosurfaces. We discuss how these pathways can potentially alter the structure at the early stages of AD, hence delaying the aggregation of amyloid-ß (Aß) and tau. We also discuss multidisciplinary approaches, combining experimental and modelling methods, that can better characterize the biochemical and biophysical interactions between proteins and phenolic ligands. In addition to the surface-induced aggregation, which can occur on surfaces where protein can interact with other proteins and polyphenols, we suggest a new concept referred as "confinement stability". Here, on the contrary, the adsorption of Aß and tau on biosurfaces other than Aß- and tau-fibrils, e.g., red blood cells, can lead to confinement stability that minimizes the aggregation of Aß and tau. Overall, these mechanisms may participate directly or indirectly in mitigating neurodegenerative diseases, by preventing protein self-association, slowing down the aggregation processes, and delaying the progression of AD.

Mitigating Alzheimer's Disease with Natural Polyphenols: A Review.

According to Alzheimer's Disease International (ADI), nearly 50 million people worldwide were living with dementia in 2017, and this number is expected to triple by 2050. Despite years of research in this field, the root cause and mechanisms responsible for Alzheimer's disease (AD) have not been fully elucidated yet. Moreover, promising preclinical results have repeatedly failed to translate into patient treatments. Until now, none of the molecules targeting AD has successfully passed the Phase III trial. Although natural molecules have been extensively studied, they normally require high concentrations to be effective; alternately, they are too large to cross the blood-brain barrier (BBB). In this review, we report AD treatment strategies, with a virtually exclusive focus on green chemistry (natural phenolic molecules). These include therapeutic strategies for decreasing amyloid-ß (Aß) production, preventing and/or altering Aß aggregation, and reducing oligomers cytotoxicity such as curcumin, (-)-epigallocatechin-3-gallate (EGCG), morin, resveratrol, tannic acid, and other natural green molecules. We also examine whether consideration should be given to potential candidates used outside of medicine and nutrition, through a discussion of two intermediate-sized green molecules, with very similar molecular structures and key properties, which exhibit potential in mitigating Alzheimer's disease.

Molecular orbital studies of gas-phase interactions between complex molecules.

Describing interactions among large molecules theoretically is a challenging task. As an example, we investigated gas-phase interactions between a linear nonionic oligomer and various model compounds (cofactors), which have been reported to associate experimentally, using PM3 semiempirical molecular orbital theory. As oligomer, we studied the hexamer of poly(ethylene oxide) (PEO), and as cofactors, we studied corilagin and related compounds containing phenolic groups (R-OH). These systems are of interest because they are models for PEO/cofactor flocculation systems, used in industrial applications. The PM3 delocalized molecular orbitals (DLMO) describe the bonding between (PEO)6 and cofactors, and some of them cover the complete complex. The DLMOs which cover the traditionally considered hydrogen bonds R-OH...O or R-CH...O show a distinct "pinch", a decrease of the electron density, between the H...O atoms. Calculations of Gibbs free energy, entropy, and enthalpy show that the PEO/cofactor complexes do not form at room temperature, because the loss of entropy exceeds the increase in enthalpy. The change in enthalpy is linearly related to the change in entropy for the different complexes. Even though bond lengths, bond angles, DLMOs, and electron densities for the PEO/cofactor complexes are consistent with the definition of hydrogen bonds, the number of intermolecular R-OH...O and R-CH...O bonds does not correlate with the enthalpy of association, indicating that the bonding mechanism for these systems is the sum of many small contributions of many delocalized orbitals.

Molecular modeling of poly(ethylene oxide) model cofactors; 1,3,6-tri-O-galloyl-beta- d-glucose and corilagin.

The most stable structures of two poly(ethylene oxide) (PEO) model cofactors, beta-1-O-galloyl-3,6-( R)-hexahydroxydiphenoyl- d-glucose (corilagin) and 1,3,6-tri-O-galloyl-beta- d-glucose (TGG), are calculated using molecular modeling and PM3 semiempirical molecular orbital theories. The theoretical PM3 structures agree with interpreted structures from experimental NMR; the glucopyranose ring of corilagin has a boat and TGG a chair conformation, for which the heats of formation, torsion angles, distances, van der Waals surface, and the infrared spectra are calculated.