Biology subjects

Scheres, S. H.

Publications and source records attributed to Scheres, S. H..

5 recordsLinked to original sources

bioRxiv2023

Data-driven regularisation lowers the size barrier of cryo-EM structure determination

Macromolecular structure determination by electron cryo-microscopy (cryo-EM) is limited by the alignment of noisy images of individual particles. Because smaller particles have weaker signals, alignment errors impose size limitations on its applicability. Here, we explore how image alignment is improved by the application of deep-learning to exploit prior knowledge about biological macromolecular structures that would otherwise be difficult to express mathematically. We train a denoising convolutional neural network on pairs of half-set reconstructions from the electron microscopy data bank (EMDB) and use this denoiser as an alternative to a commonly used smoothness prior. We demonstrate that this approach, which we call Blush regularisation, yields better reconstructions than existing algorithms, in particular for data with low signal-to-noise ratios. The reconstruction of a protein-nucleic acid complex with a molecular weight of 40 kDa, which was previously intractable, illustrates that regularisation through denoising will expand the applicability of cryo-EM structure determination for a wide range of biological macromolecules.

biophysics↗

bioRxiv2023

Cryo-EM structures of Aβ40 filaments from the leptomeninges of individuals with Alzheimer's disease and cerebral amyloid angiopathy

We used electron cryo-microscopy (cryo-EM) to determine the structures of A{beta}40 filaments from the leptomeninges of individuals with Alzheimers disease and cerebral amyloid angiopathy. In agreement with previously reported structures, which were solved to a resolution of 4.4 [A], we found three types of filaments. However, our new structures, solved to a resolution of 2.4 [A] resolution, revealed differences in the sequence assignment that redefine the fold of A{beta}40 peptides and their interactions. Filaments are made of pairs of protofilaments, the ordered core of which comprises D1-G38. The different filament types comprise one, two or three protofilament pairs. In each pair, residues H14-G37 of both protofilaments adopt an extended conformation and pack against each other in an anti-parallel fashion, held together by hydrophobic interactions and hydrogen bonds between main chains and side chains. Residues D1-H13 fold back on the adjacent parts of their own chains through both polar and non-polar interactions. There are also several additional densities of unknown identity. Sarkosyl extraction and aqueous extraction gave the same structures. By cryo-EM, parenchymal deposits of A{beta}42 and blood vessel deposits of A{beta}40 have distinct structures, supporting the view that Alzheimers disease and cerebral amyloid angiopathy are different A{beta} proteinopathies.

neuroscience↗

bioRxiv2022

New SNCA mutation and structures of α-synuclein filaments from juvenile-onset synucleinopathy

A 21-nucleotide duplication in one allele of SNCA was identified in a previously described disease with abundant -synuclein inclusions that we now call juvenile-onset synucleinopathy (JOS). Both wild-type -synuclein and its insertion mutant containing seven additional residues (MAAAEKT) after residue 22 were present in sarkosyl-insoluble material that was extracted from frontal cortex of the individual with JOS and examined by electron cryo-microscopy. The structures of JOS filaments, comprising either a single protofilament, or a pair of protofilaments, revealed a new -synuclein fold that differs from the folds of Lewy body diseases and multiple system atrophy (MSA). The JOS fold consists of a compact core, the sequence of which (residues 36-100 of wild-type -synuclein) is unaffected by the mutation, and two disconnected density islands (A and B) of mixed sequences. There is a non-proteinaceous cofactor bound between the core and island A. The JOS fold resembles the common substructure of MSA type I and type II dimeric filaments, with its core segment approximating the C-terminal body of MSA protofilaments B and its islands mimicking the N-terminal arm of MSA protofilaments A. The partial similarity of JOS and MSA folds extends to the locations of their cofactor-binding sites. Our findings provide insight into a likely mechanism of JOS fibrillation in which mutant -synuclein of 147 amino acids forms a nucleus with the JOS fold, around which wild-type and mutant proteins assemble during elongation.

neuroscience↗

bioRxiv2022

Cryo-EM structures of amyloid-beta filaments with the Arctic mutation (E22G) from human and mouse brains

The Arctic mutation, encoding E693G in the amyloid precursor protein (APP) gene [E22G in amyloid-{beta} (A{beta})], causes dominantly inherited Alzheimers disease. Here we report the high-resolution cryo-EM structures of A{beta} filaments from the frontal cortex of a previously described case (A{beta}PParc1) with the Arctic mutation. Most filaments consist of two pairs of non-identical protofilaments that comprise residues V12-V40 (human Arctic fold A) and E11-G37 (human Arctic fold B). They have a substructure (residues F20-G37) in common with the folds of type I and type II A{beta}42. When compared to the structures of wild-type A{beta}42 filaments, there are subtle conformational changes in the human Arctic folds, because of the lack of a side chain at G22, which may strengthen hydrogen bonding between mutant A{beta} molecules and promote filament formation. A minority of A{beta}42 filaments of type II was also present, as were tau paired helical filaments. In addition, we report the cryo-EM structures of A{beta} filaments with the Arctic mutation from mouse knock-in line AppNL-G-F. Most filaments are made of two identical mutant protofilaments that extend from D1-G37 (murine Arctic fold). In a minority of filaments, two dimeric folds pack against each other in an anti-parallel fashion. The murine Arctic fold differs from the human Arctic folds, but shares some substructure.

neuroscience↗

bioRxiv2022

Abundant Aβ fibrils in ultracentrifugal supernatants of aqueous extracts from Alzheimer's disease brains

Soluble aggregates of amyloid-{beta} (A{beta}), often called oligomers, are believed to be principal drivers of neurotoxicity, spreading of pathology, and symptoms in Alzheimers disease (AD), but little is known about their structures in human brain. A{beta} oligomers have been defined as aggregates found in supernatants following ultracentrifugation of aqueous extracts. We now report the unexpected presence of abundant A{beta} fibrils in high-speed supernatants from AD brains that were extracted by soaking in aqueous buffer. The fibrils did not appear to form during extract preparation, and their numbers by EM correlated with ELISA quantification of aggregated A{beta}42. Cryo-EM structures of A{beta} fibrils from aqueous extracts were identical to those from sarkosyl-insoluble AD brain homogenates. The fibrils in aqueous extracts were immunolabeled by lecanemab, an A{beta} aggregate-directed antibody reported to improve cognitive outcomes in AD. We conclude that A{beta} fibrils are abundant in aqueous extracts from AD brains and have the same structures as those from amyloid plaques. These findings have implications for understanding the nature of A{beta} oligomers and for designing oligomer-preferring therapeutic antibodies.

neuroscience↗