amyloid-beta-protein-(17-42) and Protein-Aggregation--Pathological

Fast green FCF (FGF) is often used in foods, pharmaceuticals, and cosmetics. However, little is known about the interactions of FGF with amyloid-β protein (Aβ) associated with Alzheimer's disease. In this study, the inhibitory effects of FGF on Aβ fibrillogenesis, the disruption of preformed Aβ fibrils, the reduction of Aβ-induced cytotoxicity, and the attenuation of Aβ-induced learning and memory impairments in mice were investigated. FGF significantly inhibited Aβ fibrillogenesis and disintegrated the mature fibrils as evidenced by thioflavin T fluorescence and atomic force microscopy studies. Co-incubation of Aβ with FGF greatly reduced Aβ-induced cytotoxicity in vitro. Moreover, FGF showed a protective effect against cognitive impairment in Aβ-treated mice. Molecular dynamics simulations further showed that FGF could synergistically interact with the Aβ17-42 pentamer via electrostatic interactions, hydrogen bonds and π-π interactions, which reduced the β-sheet content, and disordered random coils and bend structures of the Aβ17-42 pentamer. This study offers a comprehensive understanding of the inhibitory effects of FGF against Aβ neurotoxicity, which is critical for the search of effective food additives that can combat amyloid-associated disease.

Topics: Alzheimer Disease; Amyloid; Amyloid beta-Peptides; Animals; Cognitive Dysfunction; Exploratory Behavior; Food Additives; Humans; Hydrogen Bonding; Lissamine Green Dyes; Mice; Microscopy, Atomic Force; Models, Molecular; Molecular Dynamics Simulation; Morris Water Maze Test; Neuroprotective Agents; Peptide Fragments; Protein Aggregation, Pathological; Protein Structure, Secondary; Random Allocation; Static Electricity

Alzheimer's disease (AD) is a kind of brain disease that arises due to the aggregation and fibrillation of amyloid β-peptides (Aβ). The peptide Aβ17-42 forms U-shape protofilaments of amyloid mature fibrils by cross-β strands, detected in brain cells of individuals with AD. Targeting the structure of Aβ17-42 and destabilizing its β-strands by natural compounds could be effective in the treatment of AD patients. Therefore, the interaction features of monomeric U-shape Aβ17-42 with natural flavonoids including myricetin, morin and flavone at different mole ratios were comprehensively studied to recognize the mechanism of Aβ monomer instability using molecular dynamics (MD) simulations. We found that all flavonoids have tendency to interact and destabilize Aβ peptide structure with mole ratio-dependent effects. The interaction free energies of myricetin (with 6 OHs) and morin (with 5 OHs) were more negative compared to flavone, although the total binding energies of all flavonoids are favorable and negative. Myricetin, morin and flavone penetrated into the core of the Aβ17-42 and formed self-clusters of Aβ17-42-flavonoid complexes. Analysis of Aβ17-42-flavonoids interactions identified that the hydrophobic interactions related to SASA-dependent energy are weak in all complexes. However, the intermolecular H-bonds are a main binding factor for shifting U-shape rod-like state of Aβ17-42 to globular-like disordered state. Myricetin and morin polyphenols form H-bonds with both peptide's carbonyl and amine groups whereas flavone makes H-bonds only with amine substitution. As a result, polyphenols are more efficient in destabilizing β-sheet structures of peptide. Accordingly, the natural polyphenolic flavonoids are useful in forming stable Aβ17-42-flavonoid clusters to inhibit Aβ17-42 aggregation and these compounds could be an effective candidate for therapeutically targeting U-shape protofilaments' monomer in amyloid mature fibrils.

Topics: Alzheimer Disease; Amyloid; Amyloid beta-Peptides; Flavonoids; Humans; Hydrogen Bonding; Hydrophobic and Hydrophilic Interactions; Molecular Dynamics Simulation; Peptide Fragments; Phenols; Protective Agents; Protein Aggregation, Pathological; Protein Binding; Protein Conformation, beta-Strand; Protein Stability; Protein Structure, Tertiary

The increasing prevalence of conformational diseases, including Alzheimer's disease, type 2 Diabetes Mellitus and Cancer, poses a global challenge at many different levels. It has devastating effects on the sufferers as well as a tremendous economic impact on families and the health system. In this work, we apply a cross-functional approach that combines ideas, concepts and technologies from several disciplines in order to study, in silico and in vitro, the role of a novel chemical chaperones family (NCHCHF) in processes of protein aggregation in conformational diseases. Given that Serum Albumin (SA) is the most abundant protein in the blood of mammals, and Bovine Serum Albumin (BSA) is an off-the-shelf protein available in most labs around the world, we compared the ligandability of BSA:NCHCHF with the interaction sites in the Human Islet Amyloid Polypeptide (hIAPP):NCHCHF, and in the amyloid pharmacophore fragments (Aβ17-42 and Aβ16-21):NCHCHF. We posit that the merging of this interaction sites is a meta-structure of pharmacophore which allows the development of chaperones that can prevent protein aggregation at various states from: stabilizing the native state to destabilizing oligomeric state and protofilament. Furthermore to stabilize fibrillar structures, thus decreasing the amount of toxic oligomers in solution, as is the case with the NCHCHF. The paper demonstrates how a set of NCHCHF can be used for studying and potentially treating the various physiopathological stages of a conformational disease. For instance, when dealing with an acute phase of cytotoxicity, what is needed is the recruitment of cytotoxic oligomers, thus chaperone F, which accelerates fiber formation, would be very useful; whereas in a chronic stage it is better to have chaperones A, B, C, and D, which stabilize the native and fibril structures halting self-catalysis and the creation of cytotoxic oligomers as a consequence of fiber formation. Furthermore, all the chaperones are able to protect and recondition the cerebellar granule cells (CGC) from the cytotoxicity produced by the hIAPP20-29 fragment or by a low potassium medium, regardless of their capacity for accelerating or inhibiting in vitro formation of fibers. In vivo animal experiments are required to study the impact of chemical chaperones in cognitive and metabolic syndromes.

Topics: Amyloid beta-Peptides; Amyloidogenic Proteins; Animals; Binding Sites; Circular Dichroism; Computer Simulation; Drug Discovery; Humans; In Vitro Techniques; Microscopy, Electron, Transmission; Molecular Chaperones; Molecular Docking Simulation; Peptide Fragments; Protein Aggregation, Pathological; Serum Albumin; Serum Albumin, Bovine

Although the N-terminal region of Amyloid β (Aβ) peptides plays dual roles as metal-coordinating sites and conformational modulator, few studies have been performed to explore the effects of mutations at this region on the overall conformational ensemble of Aβ and the binding propensity of metal ions. In this work, we focus on how three familial Alzheimer's disease mutations (D7H, D7N, and H6R) alter the structural characteristics and thermodynamic stabilities of Aβ42 using molecular dynamics simulations. We observe that each mutation displays increased β-sheet structures in both N and C termini. In particular, both the N terminus and central hydrophobic region of D7H can form stable β-hairpin structures with its C terminus. The conserved turn structure at Val²⁴-Lys²⁸ in all peptides and Zn²⁺-bound Aβ42 is confirmed as the common structural motif to nucleate folding of Aβ. Each mutant can significantly increase the solvation free energy and thus enhance the aggregation of Aβ monomers. The correlation dynamics between Aβ(1-16) and Aβ(17-42) fragments are elucidated by linking the domain motions with the corresponding structured conformations. We characterize the different populations of correlated domain motions for each mutant from a more macroscopic perspective, and unexpectedly find that Zn²⁺-bound Aβ42 ensemble shares the same populations as Aβ42, indicating that the binding of Zn²⁺ to Aβ follows the conformational selection mechanism, and thus is independent of domain motions, even though the structures of Aβ have been modified at a residue level.

Topics: Alzheimer Disease; Amino Acid Substitution; Amyloid beta-Peptides; Amyloid beta-Protein Precursor; Binding Sites; Energy Transfer; Humans; Hydrophobic and Hydrophilic Interactions; Kinetics; Models, Molecular; Molecular Dynamics Simulation; Mutation; Peptide Fragments; Protein Aggregation, Pathological; Protein Conformation; Protein Folding; Protein Stability; Solubility; Surface Properties; Zinc