Protein misfolding and aggregation is observed in many amyloidogenic diseases affecting either the central nervous system or a variety of peripheral tissues. Structural and dynamic characterization of all species along the pathways from monomers to fibrils is challenging by experimental and computational means because they involve intrinsically disordered proteins in most diseases. Yet understanding how amyloid species become toxic is the challenge in developing a treatment for these diseases. Here we review what computer, in vitro, in vivo and pharmacological experiments tell us about the accumulation and deposition of the oligomers of the (Aβ, tau), α-synuclein, IAPP and superoxide dismutase 1 proteins, which have been the mainstream concept underlying Alzheimer's disease (AD), Parkinson's disease (PD), type II diabetes (T2D) and amyotrophic lateral sclerosis (ALS) research, respectively for over many years.While SOD1 is a globular protein with a well-defined 3D structure, the Aβ, tau and α-synuclein proteins belong to the class of intrinsically disordered proteins (IDPs). IDPs are also known to play a critical role in many cellular functions such as signal transduction, cell growth, binding with DNA and RNA, and transcription, and are implicated in the development of cardiovascular problems and cancers 29 . The IDPs involved in neurodegenerative diseases have a few aggregation-prone regions and overall all IDPs have a low mean hydrophobicity and a high mean net charge 30 .IDPs are structurally flexible and lack stable secondary structures in aqueous solution. When isolated, they behave as polymers in a good solvent and their radii of gyration are well described by the Flory scaling law. 31 The insolubility and high self-assembly propensity of IDPs implicated in degenerative diseases have prevented high-resolution structural determination by solution nuclear magnetic resolution (NMR) and X-ray diffraction experiments. Local information at all aggregation steps can be, however, obtained by chemical shifts, residual coupling constants, and J-couplings from NMR, exchange hydrogen/deuterium (H/D) NMR, Raman spectroscopy; and secondary structure from fast Fourier infrared spectroscopy (FTIR) or circular dichroism (CD). Long-range tertiary contacts can be deduced from paramagnetic relaxation enhancement (PRE) NMR spectroscopy and single molecule Förster resonance energy transfer (sm-FRET), and short-range distance contacts can be extracted by cross linked residues determined by mass spectrometry (MS). Low-resolution 3D information of monomers and oligomers can be obtained by ion-mobility mass-spectrometry data (IM/MS) providing cross-collision sections, dynamic light scattering (DLS), pulse field gradient NMR spectroscopy and fluorescence correlation spectroscopy (FCS) providing hydrodynamics radius, small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS), atomic force microscopy (AFM) and transmission electron microscopy (TEM) providing height features of the aggregates, as reported by some o...

She has authored over 350 scientific papers. Her interests largely focus on protein folding, protein-protein interactions, amyloid conformations, and large multimolecular associations with the goal of understanding the protein structure-function relationship.

Although a key factor in Alzheimer's disease etiology is enrichment of Zn 2þ in aggregates, and there are data suggesting that zinc promotes aggregation, how Zn 2þ -Aβ coordination promotes aggregation is elusive. Here we probe the structures and mechanisms through which Zn 2þ can affect amyloidosis. By covalently linking fragments (that have experiment-based coordinates) we observed that, in oligomeric Zn 2þ -Aβ 42 , Zn 2þ can simultaneously coordinate intra-and intermolecularly, bridging two peptides. Zinc coordination significantly decreases the solvation energy for large Zn 2þ -Aβ 42 oligomers and thus enhances their aggregation tendency. Zn 2þ binding does not change the β-sheet association around the C-terminal hydrophobic region; however, it shifts the relative population of the preexisting amyloid polymorphic ensembles. As a result, although a parallel β-sheet arrangement is still preferred, antiparallel and other less structured assemblies are stabilized, also becoming major species. Overall, Zn 2þ coordination promotes Aβ 42 aggregation leading to less uniform structures. Our replica exchange molecular dynamics simulations further reproduced an experimental observation that the increasing Zn 2þ concentration could slow down the aggregation rate, even though the aggregation rates are still much higher than in Zn 2þ -free solution.conformational selection | energy landscape | metal ions | modeling amyloid assemblies | seed polymorphism A lzheimer's disease (AD) is a progressive neurodegenerative disease and the most common cause of dementia in millions of people worldwide (1). This disease accounts for the majority of clinical senile dementia associated with the formation of senile plaques (2, 3). The primary constituent of the plaques is the aggregated Aβ 40 ∕Aβ 42 peptides in the brain; therefore, factors that influence the aggregation are of high interest.In vivo studies reported that Zn 2þ , Cu þ2 , and Fe þ3 are markedly enriched in Aβ plaques (4, 5), suggesting that these ions may act as seeding factors. Oligomerization of the Aβ peptides can be rapidly induced in the presence of Zn 2þ ions under physiological conditions (4, 6, 7). Noy et al. (8) have followed Zn 2þ ionenhanced Aβ aggregation. Studies suggested that H6, H13, and H14 at the N-terminal domain of Aβ coordinate with Zn 2þ (9-26). Solution NMR of Zn 2þ -Aβ 1-16 showed that Zn 2þ is bound to these three histidines and E11 (18). A recent NMR study of Zn 2þ -Aβ 1-28 proposed that Zn 2þ binds to H6, E11, H14, and D1 of rat Aβ 1-28 and to H6, E11, H13, H14, and D1 of human Aβ 1-28 (22). In addition, X-ray absorption spectroscopy revealed that Zn 2þ coordinates with four histidines, H13 and H14 of two adjacent monomers (23). Experimental structural data for Aβ 40 ∕Aβ 42 oligomers complexed with Zn 2þ are unavailable.Although it is believed that reducing zinc-induced Aβ aggregation can decrease toxicity (27), it was also postulated that zinc can lower Aβ toxicity by selectively precipitating aggregation intermediates (28). Key questions on the...

Cu2+ binding to Alzheimer’s β (Aβ) peptides in amyloid fibrils has attracted broad attention, as it was shown that Cu ion concentration elevates in Alzheimer’s senile plaque and such association of Aβ with Cu2+ triggers the production of neurotoxic reactive oxygen species (ROS) such as H2O2. However, detailed binding sites and binding structures of Cu2+ to Aβ are still largely unknown for Aβ fibrils or other aggregates of Aβ. In this work, we examined molecular details of Cu2+ binding to amyloid fibrils by detecting paramagnetic signal quenching in 1D and 2D high-resolution 13C SSNMR for full-length 40-residue Aβ(1–40). Selective quenching observed in 13C SSNMR of Cu2+-bound Aβ(1–40) suggested that primary Cu2+ binding sites in Aβ(1–40) fibrils include Nε in His-13 and His-14, and carboxyl groups in Val-40 as well as in Glu side chains (Glu-3, Glu-11, and/or Glu-22). 13C chemical shift analysis demonstrated no major structural changes upon Cu2+ binding in the hydrophobic core regions (residues 18–25 and 30–36). Although the ROS production via oxidization of Met-35 in the presence of Cu2+ has been long suspected, our SSNMR analysis of 13CεH3-S- in M35 showed little changes after Cu2+ binding, excluding the possibility of Met-35 oxidization by Cu2+ alone. Preliminary molecular dynamics (MD) simulations on Cu2+-Aβ complex in amyloid fibrils confirmed binding sites suggested by the SSNMR results and the stabilities of such bindings. The MD simulations also indicate the coexistence of a variety of Cu2+-binding modes unique in Aβ fibril, which are realized by both intra- and inter-molecular contacts and highly concentrated coordination sites due to the in-register parallel β-sheet arrangements.

Abeta(17-42) (so-called p3) amyloid is detected in vivo in the brains of individuals with Alzheimer's disease or Down's syndrome. We investigated the polymorphism of Abeta(17-42) oligomers based on experimental data from steady-state NMR measurements, electron microscopy, two-dimensional hydrogen exchange, and mutational studies, using all-atom molecular-dynamics simulation with explicit solvent. We assessed the structural stability and the populations. Our results suggest that conformational differences in the U-turn of Abeta(17-42) lead to polymorphism in beta-sheet registration and retention of an ordered beta-strand organization at the termini. Further, although the parallel Abeta(17-42) oligomer organization is the most stable of the conformers investigated here, different antiparallel Abeta(17-42) organizations are also stable and compete with the parallel architectures, presenting a polymorphic population. In this study we propose that 1), the U-turn conformation is the primary factor leading to polymorphism in the assembly of Abeta(17-42) oligomers, and is also coupled to oligomer growth; and 2), both parallel Abeta(17-42) oligomers and an assembly of Abeta(17-42) oligomers that includes both parallel and antiparallel organizations contribute to amyloid fibril formation. Finally, since a U-turn motif generally appears in amyloids formed by full proteins or long fragments, and since to date these have been shown to exist only in parallel architectures, our results apply to a broad range of oligomers and fibrils.

Cation diffusion facilitators (CDF) are part of a highly conserved protein family that maintains cellular divalent cation homeostasis in all domains of life. CDF's were shown to be involved in several human diseases, such as Type-II diabetes and neurodegenerative diseases. In this work, we employed a multi-disciplinary approach to study the activation mechanism of the CDF protein family. For this we used MamM, one of the main ion transporters of magnetosomes – bacterial organelles that enable magnetotactic bacteria to orientate along geomagnetic fields. Our results reveal that the cytosolic domain of MamM forms a stable dimer that undergoes distinct conformational changes upon divalent cation binding. MamM conformational change is associated with three metal binding sites that were identified and characterized. Altogether, our results provide a novel auto-regulation mode of action model in which the cytosolic domain's conformational changes upon ligand binding allows the priming of the CDF into its transport mode.

Although heterogeneous chemistry on surfaces in the troposphere is known to be important, there are currently only a few techniques available for studying the nature of surface-adsorbed species as well as their chemistry and photochemistry under atmospheric conditions of 1 atm pressure and in the presence of water vapor. We report here a new laboratory approach using a combination of long path Fourier transform infrared spectroscopy (FTIR) and attenuated total reflectance (ATR) FTIR that allows the simultaneous observation and measurement of gases and surface species. Theory is used to identify the surface-adsorbed intermediates and products, and to estimate their relative concentrations. At intermediate relative humidities typical of the tropospheric boundary layer, the nitric acid formed during NO2 heterogeneous hydrolysis is shown to exist both as nitrate ions from the dissociation of nitric acid formed on the surface and as molecular nitric acid. In both cases, the ions and HNO3 are complexed to water molecules. Upon pumping, water is selectively removed, shifting the NO(3-)-HNO3(H2O)y equilibria toward more dehydrated forms of HNO3 and ultimately to nitric acid dimers. Irradiation of the nitric acid-water film using 300-400 nm radiation generates gaseous NO, while irradiation at 254 nm generates both NO and HONO, resulting in conversion of surface-adsorbed nitrogen oxides into photochemically active NO(x). These studies suggest that the assumption that deposition or formation of nitric acid provides a permanent removal mechanism from the atmosphere may not be correct. Furthermore, a potential role of surface-adsorbed nitric acid and other species formed during the heterogeneous hydrolysis of NO2 in the oxidation of organics on surfaces, and in the generation of gas-phase HONO on local to global scales, should be considered.

Amyloid plaques and neurofibrillary tangles simultaneously accumulate in Alzheimer’s disease (AD). It is known that Aβ and tau exist together in the mitochondria; however, the interactions between Aβ oligomers and tau are controversial. Moreover, it is still unclear which specific domains in the tau protein can interact with Aβ oligomers and what could be the effect of these interactions. Herein, we examine three different Aβ–tau oligomeric complexes. These complexes present interactions of Aβ with three domains in the tau protein; all contain high β-structure propensity in their R2, R3, and R4 repeats. Our results show that, among these, Aβ oligomers are likely to interact with the R2 domain to form a stable complex with better alignment in the turn region and the β-structure domain. We therefore propose that the R2 domain can interact with soluble Aβ oligomers and consequently promote aggregation. EM and AFM images and dimensions revealed highly polymorphic tau aggregates. We suggest that the polymorphic tau and Aβ–tau aggregates may be largely due to repeat sequences which are prone to variable turn locations along the tau repeats.