Electronic DNA‐biosensor with a single nucleotide resolution capability is highly desirable for personalized medicine. However, existing DNA‐biosensors, especially single nucleotide polymorphism (SNP) detection systems, have poor sensitivity and specificity and lack real‐time wireless data transmission. DNA‐tweezers with graphene field effect transistor (FET) are used for SNP detection and data are transmitted wirelessly for analysis. Picomolar sensitivity of quantitative SNP detection is achieved by observing changes in Dirac point shift and resistance change. The use of DNA‐tweezers probe with high‐quality graphene FET significantly improves analytical characteristics of SNP detection by enhancing the sensitivity more than 1000‐fold in comparison to previous work. The electrical signal resulting from resistance changes triggered by DNA strand‐displacement and related changes in the DNA geometry is recorded and transmitted remotely to personal electronics. Practical implementation of this enabling technology will provide cheaper, faster, and portable point‐of‐care molecular health status monitoring and diagnostic devices.

Recent advances in the structural biology of disease-relevant α-synuclein fibrils have revealed a variety of structures, yet little is known about the process of fibril aggregate formation. Characterization of intermediate species that form during aggregation is crucial; however, this has proven very challenging because of their transient nature, heterogeneity, and low population. Here, we investigate the aggregation of α-synuclein bound to negatively charged phospholipid small unilamellar vesicles. Through a combination of kinetic and structural studies, we identify key time points in the aggregation process that enable targeted isolation of prefibrillar and early fibrillar intermediates. By using solid-state nuclear magnetic resonance, we show the gradual buildup of structural features in an α-synuclein fibril filament, revealing a segmental folding process. We identify distinct membrane-binding domains in α-synuclein aggregates, and the combined data are used to present a comprehensive mechanism of the folding of α-synuclein on lipid membranes.

Abstractα-synuclein misfolding and aggregation into fibrils is a common feature of α-synucleinopathies, such as Parkinson’s disease, in which α-synuclein fibrils are a characteristic hallmark of neuronal inclusions called Lewy bodies. Studies on the composition of Lewy bodies extracted postmortem from brain tissue of Parkinson’s patients revealed that lipids and membranous organelles are also a significant component. Interactions between α-synuclein and lipids have been previously identified as relevant for Parkinson’s disease pathology, however molecular insights into their interactions have remained elusive. Here we present cryo-electron microscopy structures of six α-synuclein fibrils in complex with lipids, revealing specific lipid-fibril interactions. We observe that phospholipids promote an alternative protofilament fold, mediate an unusual arrangement of protofilaments, and fill the central cavities of the fibrils. Together with our previous studies, these structures also indicate a mechanism for fibril-induced lipid extraction, which is likely to be involved in the development of α-synucleinopathies. Specifically, one potential mechanism for the cellular toxicity is the disruption of intracellular vesicles mediated by fibrils and oligomers, and therefore the modulation of these interactions may provide a promising strategy for future therapeutic interventions.

Aggregation of amyloidogenic proteins is a characteristic of multiple neurodegenerative diseases. Atomic resolution of small molecule binding to such pathological protein aggregates is of interest for the development of therapeutics and diagnostics. Here we investigate the interaction between α-synuclein fibrils and anle138b, a clinical drug candidate for disease modifying therapy in neurodegeneration and a promising scaffold for positron emission tomography tracer design. We used nuclear magnetic resonance spectroscopy and the cryogenic electron microscopy structure of α-synuclein fibrils grown in the presence of lipids to locate anle138b within a cavity formed between two β-strands. We explored and quantified multiple binding modes of the compound in detail using molecular dynamics simulations. Our results reveal stable polar interactions between anle138b and backbone moieties inside the tubular cavity of the fibrils. Such cavities are common in other fibril structures as well.

α-synuclein (αSyn) is abundant in neurons, but its misfolding and abnormal fibrillization are associated with severe neurodegenerative diseases. Although interactions between αSyn and phospholipid membranes are relevant during αSyn fibril assembly, insights into the interactions of αSyn fibrils with phospholipids have remained elusive. Here, we present six novel polymorphic atomic structures of αSyn fibrils aggregated in the presence of phospholipids. The structures reveal that phospholipids favor a novel protofilament fold, mediate an unusual arrangement of protofilaments, and fill the central cavities between the protofilaments. These findings provide a structural rationale for fibril-induced lipid extraction, a mechanism likely to be involved in the development of α-synucleinopathies.

Low-molecular weight oligomers of amyloid-b (Ab) peptides have emerged as primary toxic species involved in the Alzheimer disease (AD) pathogenesis. Recent findings suggest that oligomers of distinct conformations could self-propagate toward specific aggregate structures. Regarding the generation of specific oligomer conformers, the association of Ab with lipids play an important role. In our laboratory, we investigate the role of membrane lipids and surfactants in modulating Ab aggregation to generate distinct oligomer strains. We hypothesize that such strains that vary in biophysical & biochemical properties, could also lead to specific phenotypes in brains. Growing evidence indicate prion-like progression of Ab aggregate seeds that give rise to specific clinicopatholologic phenotypes in the AD. We investigated the characteristics of Ab oligomers generated in the presence of various ganglioside & anionic phospholipid micelles/liposomes invitro. We found that the Ab peptides interact uniquely with gangliosides and other anionic phospholipids. However, all the oligomers were found to be parallel b-sheet rich with similar molecular weight and hydrodynamic diameter. We also observed distinct range of melting temperatures for all lipid -derived oligomers indicating that they have similar thermodynamic stabilities. Together, these findings indicate that the lipid -derived oligomers may be a part of a distinct class of oligomer strains that could result in a common AD phenotype.

The horseshoe conformation of the membrane-bound form of alpha-synuclein (aS) is a still controversial. Here we reinvestigate distance distributions from DEER of aS bound to IMM and the NPM membranes [1]. With aS spin labelled at residues 27 and 56, two-component distance distributions were found, with distances of 4.3 nm, extended conformation of aS, and 3.6 nm. The latter distance was attributed to an expanded horseshoe conformation [1], because it was longer than the 2.6 nm distance obtained for aS27/56 in the horseshoe conformation on artificial membranes [2] and micelles. The DEER distance distributions, obtained by Tikhonov regularization, have two maxima, separated by a trough (Figs 2C and D in [1]). Reanalysis of these data using the Bayesian approach [3] shows that the distance distributions from aS on IMM and NPM are similar to each other, in agreement with the conclusions of [1]. However, the trough between the two maxima is not significant. Therefore, the distance distributions should be interpreted as broad, continuous distributions, not as two distinct distances. For aS membrane binding, this implies that rather than two distinct conformations, aS has a continuum of conformations, between the extended and a more bent conformation, but does not bend as far as the previously determined horseshoe conformation [2]. This demonstrates that analysis of DEER primary data by statistical approaches contributes crucial knowledge about the distance distribution and in the present case changes the interpretation.

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