Interaction with zinc oxide nanoparticle kinetically traps α-synuclein fibrillation into off-pathway non-toxic intermediates.

α-Synuclein is an intrinsically disordered amyloidogenic protein associated with Parkinson's disease (PD). The monomeric α-synuclein transition into amyloid fibril involves multiple steps, which are affected by several intrinsic and extrinsic factors. This increases complexities in development of targeted therapeutics against the pathological intermediate(s). Several studies have been dedicated to find an effective molecule to inhibit the detrimental amyloidogenesis. In recent years, metal oxide nanoparticle interfaces have shown direct effects on protein conformation, hence may be adopted as an alternative potential therapeutic approach against amyloidosis. In this context, our study explores the zinc oxide nanoparticle (ZnONP) with negative surface potential interface interaction with α-synuclein, and subsequent impact of the interaction on the protein fibrillation and the fibril-mediated cytotoxicity. N-terminus amphipathic "KA/TKE/QGV" repeating motifs in α-synuclein primarily interact with the ZnONP interface that enthalpically drives initial adsorption of the protein onto the interface. Whereas, subsequent bulk-protein adsorption onto the hard-corona is entropically driven, leading into flocculation of the complex. The flocs appear as amorphous mesh-like morphology in TEM micrographs, as opposed to the typical fibrils formed by the wild-type protein. Interestingly, α-synuclein in complex with ZnONP shows significantly lowered cytotoxicity against the IMR32 and THP-1 cells in-vitro, as compared to fresh α-synuclein.

Insulin adsorption onto zinc oxide nanoparticle mediates conformational rearrangement into amyloid-prone structure with enhanced cytotoxic propensity.

BACKGROUND: Injection localized amyloidosis is one of the most prevalent disorders in type II diabetes mellitus (TIIDM) patients relying on insulin injections. Previous studies have reported that nanoparticles can play a role in the amyloidogenic process of proteins. Hence, the present study deals with the effect of zinc oxide nanoparticles (ZnONP) on the amyloidogenicity and cytotoxicity of insulin. METHODS: ZnONP is synthesised and characterized using XRD, Zeta Sizer, UV-Visible spectroscope and TEM. The characterization is followed by ZnONP interaction with insulin, which is studied employing fluorescence spectroscopes, isothermal titration calorimetry and molecular dynamics simulations. The interaction leads insulin conformational rearrangement into amyloid-like fibril, which is studied using thioflavin T dye binding assay, circular dichroism spectroscopy and TEM, followed by cytotoxicity propensity using Alamar Blue dye reduction assay. RESULTS: Insulin has very weak interaction with ZnONP interface. Insulin at studied concentration forms amorphous aggregates at physiological pH, whereas in presence of ZnONP interface amyloid-like fibrils are formed. While the amyloid-like fibrils are cytotoxic to MIN6 and THP-1 cell lines, insulin and ZnONP individual solutions and their fresh mixtures enhance the cells proliferation. CONCLUSIONS: The presence of ZnONP interface enhances insulin fibrillation at physiological pH by providing a favourable template for the nucleation and growth of insulin amyloids. GENERAL SIGNIFICANCE: The studied protein-nanoparticle system from protein conformational dynamics point of view throws caution over nanoparticle use in biological applications, especially in vivo applications, considering the amyloidosis a very slow but non-curable degenerative disease.

The smaller heparin fragments bind non-specifically through the IAPP sequence: An in silico study.

The diminishing ß-cell mass of pancreas in type II diabetes mellitus (TIIDM) is intricately linked with high fibrillation propensity of islet amyloid polypeptide (IAPP, aka amylin). IAPP is one of the most amyloidogenic peptide secreted by pancreatic ß-cells. In the autopsy of TIIDM patients, IAPP rich amyloid plaques are found containing different components of extracellular matrix (ECM), including heparin. For a positively charged IAPP, interaction with heparin which has accessible high density negatively charged functional groups is anticipated to moderate the fibrillation kinetics. Hence, the heparin has shown to affect the amyloidogenicity and cytotoxicity of IAPP depending upon its polymer length; short polymer inhibited the amyloidogenicity and longer fragment enhanced the propensity. Here using docking and molecular dynamic (MD) simulations studies, the work investigates key interactions between IAPP and different heparin fragments, those are likely involved in moderating IAPP fibrillation kinetics in presence of different length heparin fragments. The findings indicate that the heparin fragments of longer length, >dp7, predominantly interact with IAPP N- and C-termini, resulting in a stable complex with solvent accessible self-recognition element (SRE) of IAPP sequence. However, shorter fragment non-specifically binds through the IAPP sequence, including N-terminus residues and SRE sequences.