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Antiparallel triple-strand architecture for prefibrillar A?42 oligomers.

ABSTRACT: A?42 oligomers play key roles in the pathogenesis of Alzheimer disease, but their structures remain elusive partly due to their transient nature. Here, we show that A?42 in a fusion construct can be trapped in a stable oligomer state, which recapitulates characteristics of prefibrillar A?42 oligomers and enables us to establish their detailed structures. Site-directed spin labeling and electron paramagnetic resonance studies provide structural restraints in terms of side chain mobility and intermolecular distances at all 42 residue positions. Using these restraints and other biophysical data, we present a novel atomic-level oligomer model. In our model, each A?42 protein forms a single ?-sheet with three ?-strands in an antiparallel arrangement. Each ?-sheet consists of four A?42 molecules in a head-to-tail arrangement. Four ?-sheets are packed together in a face-to-back fashion. The stacking of identical segments between different ?-sheets within an oligomer suggests that prefibrillar oligomers may interconvert with fibrils via strand rotation, wherein ?-strands undergo an ?90° rotation along the strand direction. This work provides insights into rational design of therapeutics targeting the process of interconversion between toxic oligomers and non-toxic fibrils.

SUBMITTER: Gu L

PROVIDER: S-EPMC4175361 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature

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Antiparallel triple-strand architecture for prefibrillar Aβ42 oligomers.

Gu Lei L Liu Cong C Stroud James C JC Ngo Sam S Jiang Lin L Guo Zhefeng Z

The Journal of biological chemistry 20140812 39

Aβ42 oligomers play key roles in the pathogenesis of Alzheimer disease, but their structures remain elusive partly due to their transient nature. Here, we show that Aβ42 in a fusion construct can be trapped in a stable oligomer state, which recapitulates characteristics of prefibrillar Aβ42 oligomers and enables us to establish their detailed structures. Site-directed spin labeling and electron paramagnetic resonance studies provide structural restraints in terms of side chain mobility and inter ...[more]

PMID: 25118290

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Project description:Transthyretin (TTR) is a protein linked to a number of different amyloid diseases including senile systemic amyloidosis and familial amyloidotic polyneuropathy. The transient nature of oligomeric intermediates of misfolded TTR that later mature into fibrillar aggregates makes them hard to study, and methods to study these species are sparse. In this work we explore a novel pathway for generation of prefibrillar aggregates of TTR, which provides important insight into TTR misfolding. Prefibrillar amyloidogenic oligomers and protofibrils of misfolded TTR were generated in vitro through induction of the molten globule type A-state from acid unfolded TTR through the addition of NaCl. The aggregation process produced fairly monodisperse oligomers (300-500 kD) within 2 h that matured after 20 h into larger spherical clusters (30-50 nm in diameter) and protofibrils as shown by transmission electron microscopy. Further maturation of the aggregates showed shrinkage of the spheres as the fibrils grew in length, suggesting a conformational change of the spheres into more rigid structures. The structural and physicochemical characteristics of the aggregates were investigated using fluorescence, circular dichroism, chemical cross-linking, and transmission electron microscopy. The fluorescent dyes 1-anilinonaphthalene-8-sulfonate (ANS), 4-4-bis-1-phenylamino-8-naphthalene sulfonate (Bis-ANS), 4-(dicyanovinyl)-julolidine (DCVJ), and thioflavin T (ThT) were employed in both static and kinetic assays to characterize these oligomeric and protofibrillar states using both steady-state and time-resolved fluorescence techniques. DCVJ, a molecular rotor, was employed for the first time for studies of an amyloidogenic process and is shown useful for detection of the early steps of the oligomerization process. DCVJ bound to the early prefibrillar oligomers (300-500 kD) with an apparent dissociation constant of 1.6 muM, which was slightly better than for ThT (6.8 muM). Time-resolved fluorescence anisotropy decay of ANS was shown to be a useful tool for giving further structural and kinetic information of the oligomeric aggregates. ThT dramatically increases its fluorescence quantum yield when bound to amyloid fibrils; however, the mechanism behind this property is unknown. Data from this work suggest that unbound ThT is also intrinsically quenched and functions similarly to a molecular rotor, which in combination with its environmental dependence provides a blue shift to the characteristic 482 nm wavelength when bound to amyloid fibrils.

Dataset Information

Antiparallel triple-strand architecture for prefibrillar A?42 oligomers.

Publications

Antiparallel triple-strand architecture for prefibrillar Aβ42 oligomers.

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