interactions-with-membrane-permeabilization-brain-mitochondria

Interactions with and Membrane Permeabilization of Brain Mitochondria by Amyloid Fibrils

A growing body of evidence indicates that membrane permeabilization, including internal membranes such as mitochondria, is a common feature and primary ...

Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, 45137-66731, Iran

Increasing body of evidence suggests that polyphenols frequently interacting with amyloid aggregates and/or interfering with aggregate species to bind biomembranes may serve as a therapeutic approach for the treatment of amyloid-related diseases. Hence, in the present study, the possible effects of three naturally occurring polyphenols including Curcumin, Quercetin, and Resveratrol on mitochondrial membrane permeabilization induced by Hen Egg White Lysozyme (HEWL) oligomers were investigated. Our results indicated that pre-incubation of mitochondrial homogenate with polyphenols considerably inhibit membrane permeabilization in a concentration dependent manner. In parallel, HEWL oligomers, which were co-incubated with the polyphenols, showed less effectiveness on membrane permeabilization, suggesting that toxicity of oligomers was hindered. Using a range of techniques including fluorescence quenching, Nile red binding assay, zeta potential and size measurements, CD (far- and near-UV) spectroscopy, and molecular docking, we found that the polyphenols, structure-dependently, interact with and induce conformational changes in HEWL oligomers, thereby inhibit their toxicity. We proposed a mechanism by which selected polyphenols induce their protective effects through binding to mitochondria and interfering with HEWL oligomer-membrane interactions and/or by direct interaction with HEWL oligomers, induction of conformational changes, and generating far less toxic species. However, additional studies are needed to elucidate the detailed mechanisms involved.

Polyphenols protect mitochondrial membrane against permeabilization induced by HEWL oligomers: Possible mechanism of action.

Post-translational modifications play important roles in conformational properties and aggregation propensities of different peptides and proteins. In the present study, we have investigated the effects of acetylation of lysine residues on the structure and aggregation properties of apomyoglobin (apoMb).All of the 19 lysine residues were modified. Far-, near-UV CD, intrinsic and acrylamide quenching fluorescence studies indicated that acetylation significantly influences conformation of apoMb by altering both its secondary and tertiary structures. A considerable decrease in ANS fluorescence intensity was observed, which also suggested disruption of the heme pocket. Dynamic light scattering indicated partial compaction of protein structure as a consequence of the shielding effect of acetylation. While the presence of well-defined mature fibrils was detected in solutions of native apoMb, acetylation promoted formation of non-toxic amorphous aggregates, with low β-sheets content and decreased affinity for Thioflavin T, an amyloid-specific dye. Results are discussed in terms of the role of surface charge in conformational alterations of proteins and how small changes in ionic networks may affect aggregation pathways and morphology of the resulting aggregates. The physiological significance of the modification process in controlling cytotoxicity of the aggregated species is also discussed.

Acetylation of lysine residues in apomyoglobin: Structural changes, amyloid fibrillation, and role of surface charge.

In the present study, we have investigated the effects of protein concentration and stirring on the in vitro assembly of Hen Egg White Lysozyme (HEWL), particularly with regard to the aggregate morphology and anti-amyloidogenic properties of two naturally occurring polyphenols, taxifolin and silibinin. The results obtained clearly demonstrated that applying stirring and concentration enhancement alter the amount as well as morphology of amyloid fibrils formed. Additionally, latter aggregates exhibited higher affinity for amyloid-specific dyes. The second part of the present investigation was devoted to studies involving anti-amyloidogenic properties of selected polyphenols. Importantly, we found that the potency of polyphenols to inhibit HEWL amyloid fibrillation and related toxicity is strongly dependent on the amyloidogenic conditions in which amyloid fibrils are produced. Based on obtained data, under condition where the rate of protein assembly is high (higher protein concentration and stirring), the capacity of polyphenols to inhibit HEWL fibrillogenesis and related cytotoxicity may dramatically decrease. Similar results were obtained when we used taxifolin to inhibit bovine insulin amyloid fibrillation. Additionally, amyloidogenic conditions may also affect the mechanism by which these molecules inhibit HEWL fibrillation. The possible mechanism by which selected polyphenols exert their inhibitory effects, under various experimental conditions, is also discussed.

Article	Year
Polyphenols protect mitochondrial membrane against permeabilization induced by HEWL oligomers: Possible mechanism of action. International journal of biological macromolecules\| PubMed ID: 28545969	2017
Acetylation of lysine residues in apomyoglobin: Structural changes, amyloid fibrillation, and role of surface charge. International journal of biological macromolecules\| PubMed ID: 28919529	2018
Effect of fibrillation conditions on the anti-amyloidogenic properties of polyphenols and their involved mechanisms. International journal of biological macromolecules\| PubMed ID: 29949746	2018

Ali Akbar Meratan

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