Biology subjects

Diamond, M. I.

Publications and source records attributed to Diamond, M. I..

At least 19 recordsLinked to original sources

bioRxiv2026

An N-terminal ATTR Fibril Segment Promotes Transthyretin Amyloid Nucleation and Polymorphism

ATTR amyloidosis is caused by transthyretin (TTR) amyloid deposition, yet the sequence-encoded events linking TTR misfolding to fibril nucleation and structural polymorphism remain incompletely defined. Here, we exploit the modular organization of patient-derived TTR fibrils to investigate two components of the pathological core: an N-terminal beta-hairpin spanning residues 11-35 (N-TTR) and a larger C-terminal fragment spanning residues 57-123 (C-TTR). Both fragments independently form beta-rich amyloid fibrils, as demonstrated by electron microscopy, circular dichroism, and fluorescence spectroscopy. Yet, their activities differ markedly. N-TTR fibrils promote full-length TTR aggregation and seed in an engineered cellular biosensor platform established to detect templated TTR assembly, whereas C-TTR aggregates show no detectable templating activity. Cryo-electron microscopy reveals two N-TTR polymorphs that preserve structural features of disease-derived folds, while energetic profiling identifies N-TTR as a stabilizing hotspot within ex vivo structures, providing a basis for this templating functionality. These findings reveal a functional hierarchy among amyloidogenic segments of TTR, since distinct regions form fibrils independently, but only those with structural compatibility efficiently template the parent protein. N-TTR therefore represents an autonomous amyloidogenic segment that links local sequence propensity to TTR nucleation, templating, and fibril polymorphism.

biophysics↗

bioRxiv2026

A functional amyloid scaffold shapes insect egg coats

Functional amyloids serve as structural scaffolds across biology, yet the molecular architecture and assembly principles of many remain unresolved. The lepidopteran egg coat, or chorion, presents a striking example: hundreds of paralogous proteins sharing a conserved central domain form a mechanically resilient amyloid matrix essential for embryo protection. Here, combining evolutionary analysis of more than 500 sequences with cryo-electron microscopy and biophysical assays, we determine the atomic structure of chorion amyloid filaments and uncover the principles governing their assembly. Contrary to previous structural predictions, chorion filaments adopt a {beta}-serpentine fold stabilized by a short hexapeptide motif that forms homotypic steric-zipper interfaces, self-assembles autonomously, and seeds full-length filament growth. Amyloid formation proceeds through secondary nucleation, while thermodynamic and structural analyses support a hierarchical assembly mechanism in which motif-driven interactions nucleate filament formation prior to consolidation of the mature yet lalbile protofilament core. These findings establish the molecular basis of insect egg-coat assembly and demonstrate that mechanisms commonly associated with pathological aggregation can also operate within a biologically regulated functional amyloid framework.

biophysics↗

bioRxiv2026

Cysteines are critical determinants of spontaneous and seeded tau aggregation in cells

The frontotemporal dementia-linked S320F mutation in the microtubule-associated protein tau promotes spontaneous aggregation, yet the structural basis of its amyloidogenesis remains unclear. Using cryo-electron microscopy, we determined the structure of an S320F295-330 tau fibril composed of parallel chains stabilized by the 306VQIVYK311 amyloid motif, with S320F buried in the fibril core and a C322-C322 disulfide linking two protofilaments. Although cysteines are dispensable for fibril formation by isolated peptide fragments in vitro, tau repeat domain constructs containing both C291 and C322 generate more potent seeds in cellular assays. In contrast, the C322S mutation suppresses spontaneous aggregation of S320F tau in cells, and combined C291S and C322S mutations inhibit seeded aggregation in both wild-type and S320F contexts. Systematic alanine mutagenesis coupled with seeding by tauopathy-derived material identifies cysteine residues as critical determinants of tau seeding, comparable in importance to core amyloid motifs. Together, these findings establish cysteines as central chemical regulators of tau aggregation and propagation.

biophysics↗

bioRxiv2025

Guam amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) features CTE-like tau seeds in brain and spinal cord

Amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) is a fatal neurodegenerative disorder that was once hyperendemic in the island of Guam (Mariana Islands, US) and a few other Pacific locales. Despite extensive investigations into its origins, the etiology of ALS/PDC remains unclear. ALS/PDC is, at the neuropathology level, characterized by tau-dominant multiple proteinopathy in brain and spinal cord. It was recently reported that Guam ALS/PDC brain extracts exhibit tau seeding activity in fluorescence resonance energy transfer (FRET)-based biosensor cells. To build upon those findings and explore the nature of tau seeds in ALS/PDC in more detail, we used an alanine mutational scanning (Ala scan) approach to determine the seeding profile of tau in nervous tissues of Guam ALS/PDC cases. First, we confirmed the detection of tau seeding activity in ALS/PDC brain samples in tau biosensor cells. Notably, we could also detect potent tau seeding activity in spinal cord. Subsequent Ala scan assays demonstrated that ALS/PDC tau displays an aggregate incorporation pattern that resembles that of chronic traumatic encephalopathy (CTE)-type tau. This result is consistent with recent electron cryo-microscopy studies of tau, which revealed that ALS/PDC tau filaments are predominantly of the CTE-type. The structural characteristics and seeding behavior of ALS/PDC tau, as well as the regional distribution of tau pathology at post-mortem, suggest that ALS/PDC is a CTE-like tauopathy. Significance StatementNeurodegenerative tauopathies are characterized by proteinaceous deposits containing microtubule-associated tau in nervous tissue. Emerging evidence suggests that disease-associated tau proteins adopt abnormal, self-propagating conformations characteristic of prions. Here, we employed alanine mutational scanning (Ala scan) to determine the nature of prion-like tau seeds in ALS/PDC, a mysterious disorder that occurred formerly in high incidence in certain regions in the western Pacific. We show that the Ala scan incorporation profile of ALS/PDC tau is similar to that of abnormal tau proteins in chronic traumatic encephalopathy (CTE). The findings lend support to the idea that ALS/PDC can be classified structurally as a CTE-like tauopathy. This work may have important implications for our understanding of ALS/PDC as well as common neurological disorders beyond the Pacific.

neuroscience↗

bioRxiv2025

TAF15 amyloids propagate via defined motifs in a prion-like fashion

TATA-box binding protein-associated factor 15 (TAF15) is an RNA-binding member of the FET family recently identified as the primary fibrillar constituent in a subset of frontotemporal lobar degeneration (FTLD-FET) cases. Although TAF15 is also linked to amyotrophic lateral sclerosis (ALS), the molecular basis and propagation behavior of its aggregates remain unknown. In this work, we show that recombinant TAF15 forms amyloid fibrils under physiological conditions and developed a single-fluorophore TAF15 biosensor to quantitatively monitor their cellular propagation. Using this system, we demonstrate that both recombinant TAF15 fibrils and pathological aggregates extracted from atypical FTLD with ubiquitin inclusions (aFTLD-U) patient brains seed aggregation efficiently and transmit serially between cells, demonstrating hallmark features of prion-like propagation. Seeding was specific to TAF15 and absent for other amyloidogenic proteins, including the homologous protein fused-in-sarcoma (FUS), revealing an unexpected cross-seeding barrier. Occasional colocalization of FUS within TAF15 inclusions was observed upon transient co-expression, suggesting that FUS can be passively recruited rather than acting as an inducer of pathology in FTLD-FET brains. Computational and peptide-based experimental mapping identified multiple aggregation-prone regions within the TAF15 low-complexity domain that coincide with hotspots stabilizing the core of ex vivo TAF15 amyloid fibrils. These short motifs encode the propagation propensity of TAF15 aggregation in vitro and in cells. Together, these findings establish TAF15 as a bona fide amyloid-forming, prion-like protein and define the sequence grammar underlying its self-assembly, providing a mechanistic framework for its role in FTLD-FET and ALS and offering tractable molecular targets for therapeutic intervention.

biophysics↗

bioRxiv2025

TDP-43 Aggregate Seeding Impairs Autoregulation and Causes TDP-43 Dysfunction

The aggregation, cellular mislocalization and dysfunction of TDP-43 are hallmarks of multiple neurodegenerative disorders. We find that inducing TDP-43 aggregation through prion-like seeding gradually diminishes normal TDP-43 nuclear localization and function. Aggregate-affected cells show signature features of TDP-43 loss of function, such as DNA damage and dysregulated TDP-43-target expression. We also observe strong activation of TDP-43-controlled cryptic exons in cells, including human neurons treated with proteopathic seeds. Furthermore, aggregate seeding impairs TDP-43 autoregulation, an essential mechanism controlling TDP-43 homeostasis. Interestingly, proteins that normally interact with TDP-43 are not recruited to aggregates, while other factors linked to TDP-43 pathology, including Ataxin 2, specifically colocalize to inclusions and modify seeding-induced aggregation. Our findings indicate that TDP-43 aggregation, mislocalization and loss of function are strongly linked and suggest that disruption of TDP-43 autoregulation establishes a toxic feed-forward mechanism that amplifies aggregation and may be central in mediating this pathological connection.

cell biology↗

bioRxiv2025

Selective Targeting of Pathogenic Tau Seeds via a Novel VHH

In Alzheimers disease (AD) and related tauopathies, progressive pathology has been linked to prion mechanisms, whereby ordered tau assemblies, or "seeds," form in one cell and transit to neighboring or connected cells where they serve as templates for their own replication. Despite intensive efforts to develop early diagnosis and effective treatment, none has emerged. This is due partly to the structural heterogeneity of tau seeds and limitations in selectively targeting their pathogenic conformations. Here we report the discovery of a camelid variable heavy domain of heavy chain (VHH) that preferentially binds tau seeds of AD, corticobasal degeneration (CBD), and PS19 tauopathy mouse brains. From a published synthetic VHH yeast display library, we identified VHH clones that bound 2N4R tau monomer. After counter-screening for immunoprecipitation of seeding from human brain, we identified two seed-selective anti-tau VHH--VHH(510) and VHH(50)--that preferentially bound pathological tau. We enhanced the stability of these VHHs through framework mutations without affecting their seed-binding characteristics. We characterized VHH(510) in detail, determining that it binds the carboxy terminus of tau, maintains robust seed avidity even in the presence of competing monomer, and stains pathological tau inclusions in mouse and human AD tissues. These results highlight the power of seed-selective VHH to bind pathogenic tau, paving the way for future therapeutic and diagnostic applications across a wide range of neurodegenerative disorders.

neuroscience↗

bioRxiv2024

Essential tremor with tau pathology features seeds indistinguishable in conformation from Alzheimer's disease and primary age-related tauopathy

Neurodegenerative tauopathies are characterized by the deposition of distinct fibrillar tau assemblies whose rigid core structures correlate with defined neuropathological phenotypes. Essential tremor (ET) is a progressive neurological disease disease that, in some cases, is associated with cognitive impairment and tau accumulation.. Consequently, we explored the tau assembly conformation in ET patients with tau pathology using cytometry-based tau biosensor assays. These assays quantify tau prion seeding activity present in brain homogenates based on conversion of intracellular tau-fluorescent protein fusions from a soluble to an aggregated state. Prions exhibit seeding barriers, whereby a specific assembly structure cannot serve as a template for a native monomer if the amino acids are not compatible. We recently exploited the tau prion species barrier to define tauopathies by systematically substituting alanine (Ala) in the tau monomer and measuring its incorporation into seeded aggregates within biosensor cells. The Ala scan precisely classified the conformation of tau seeds from diverse tauopathies. We next studied 18 ET patient brains with tau pathology. Only one case had concurrent high amyloid-{beta} plaque pathology consistent with Alzheimers disease (AD). We detected robust tau seeding activity in 9 (50%) of the patients. This predominantly localized to the temporal pole and temporal cortex. We examined 8 ET cases with the Ala scan and determined that the amino acid requirements for tau monomer incorporation into aggregates seeded from these ET brain homogenates were identical to those of AD and primary age-related tauopathy (PART), and completely distinct from other tauopathies such as corticobasal degeneration, chronic traumatic encephalopathy, and progressive supranuclear palsy. Based on these studies, tau assembly cores in a pathologically confined subset of ET cases with high tau pathology are identical to AD and PART. This could facilitate more precise diagnosis and therapy for ET patients with cognitive impairment.

pathology↗

bioRxiv2024

Functional classification of tauopathy strains reveals the role of protofilament core residues.

Distinct tau amyloid assemblies underlie diverse tauopathies but defy rapid classification. Cell and animal experiments indicate tau functions as a prion, as different strains propagated in cells cause unique, transmissible neuropathology after inoculation. Strain amplification requires compatibility of the monomer and amyloid template. We used cryo-EM to study one cell-based YFP-tagged strain, resolving its amyloid nature. We then used sequential alanine (Ala) substitution (scan) within tau repeat domain (RD) to measure incorporation to pre-existing tau RD-YFP aggregates. This robustly discriminated strains, defining sequences critical for monomer incorporation. We then created 3R/4R or 4R WT RD (aa 246-408) biosensors. Ala scan of recombinant tau seeds with the Alzheimers Disease fold matched that of AD homogenate. We scanned 22 brain lysates comprising 4 tauopathies. This clustered cases by neuropathological syndrome, revealed the role of amino acids in protofilament folds, and allowed strain discrimination based on amino acid requirements for prion replication. TeaserDiscrimination of tau strains based on the relative contribution of each amino acid to templated propagation of the amyloid.

neuroscience↗

bioRxiv2023

Docking for molecules that bind in a symmetric stack with SymDOCK

Discovering ligands for amyloid fibrils, such as those formed by the tau protein, is an area of much current interest. In recent structures, ligands bind in stacks in the tau fibrils to reflect the rotational and translational symmetry of the fibril itself; in these structures the ligands make few interactions with the protein but interact extensively with each other. To exploit this symmetry and stacking, we developed SymDOCK, a method to dock molecules that follow the proteins symmetry. For each prospective ligand pose, we apply the symmetry operation of the fibril to generate a self-interacting and fibril-interacting stack, checking that doing so will not cause a clash between the original molecule and its image. Absent a clash, we retain that pose and add the ligand-ligand van der Waals energy to the ligands docking score (here using DOCK3.8). We can check these geometries and energies using an implementation of ANI, a neural network-based quantum-mechanical evaluation of the ligand stacking energies. In retrospective calculations, symmetry docking can reproduce the poses of three tau PET tracers whose structures have been determined. More convincingly, in a prospective study SymDOCK predicted the structure of the PET tracer MK-6240 bound in a symmetrical stack to AD PHF tau before that structure was determined; the docked pose was used to determine how MK-6240 fit the cryo-EM density. In proof-of-concept studies, SymDOCK enriched known ligands over property-matched decoys in retrospective screens without sacrificing docking speed, and can address large library screens that seek new symmetrical stackers. Future applications of this approach will be considered.

biophysics↗

bioRxiv2023

Cryo-EM structure of Alzheimer disease tau filaments with PET ligand MK-6240

Positron Emission Tomography (PET) ligands have advanced Alzheimers disease (AD) diagnosis and treatment. Using autoradiography and cryo-EM, we identified AD brain tissue with elevated tau burden, purified filaments, and determined the structure of second-generation high avidity PET ligand MK-6240 at 2.31 [A] resolution, which bound at a 1:1 ratio within the cleft of tau paired-helical filament (PHF), engaging with glutamine 351, lysine K353, and isoleucine 360. This information elucidates the basis of MK-6240 PET in quantifying PHF deposits in AD and may facilitate the structure-based design of superior ligands against tau amyloids.

neuroscience↗

bioRxiv2023

VCP increases or decreases tau seeding using specific cofactors

BackgroundNeurodegenerative tauopathies may progress based on seeding by pathological tau assemblies, whereby an aggregate is released from one cell, gains entry to an adjacent or connected cell, and serves as a specific template for its own replication in the cytoplasm. In vitro seeding reactions typically take days, yet seeding into the complex cytoplasmic milieu can happen within hours. A cellular machinery might regulate this process, but potential players are unknown. MethodsWe used proximity labeling to identify factors that control seed amplification. We fused split-APEX2 to the C-terminus of tau repeat domain (RD) to reconstitute peroxidase activity upon seeded intracellular tau aggregation. We identified valosin containing protein (VCP/p97) 5h after seeding. Mutations in VCP underlie two neurodegenerative diseases, multisystem proteinopathy and vacuolar tauopathy, but its mechanistic role is unclear. We utilized tau biosensors, a cellular model for tau aggregation, to study the effects of VCP on tau seeding. ResultsVCP knockdown reduced tau seeding. However, distinct chemical inhibitors of VCP and the proteasome had opposing effects on aggregation, but only when given <8h of seed exposure. ML-240 increased seeding efficiency [~]40x, whereas NMS-873 decreased seeding efficiency by 50%, and MG132 increased seeding [~]10x. We screened VCP co-factors in HEK293 biosensor cells by genetic knockout or knockdown. Reduction of ATXN3, NSFL1C, UBE4B, NGLY1, and OTUB1 decreased tau seeding, as did NPLOC4, which also uniquely increased soluble tau levels. Reduction of FAF2 and UBXN6 increased tau seeding. ConclusionsVCP uses distinct cofactors to determine seed replication efficiency, consistent with a dedicated cytoplasmic processing complex that directs seeds towards dissolution vs. amplification.

cell biology↗

bioRxiv2023

Endogenous recapitulation of Alzheimers disease neuropathology through human 3D direct neuronal reprogramming

Alzheimers disease (AD) is a neurodegenerative disorder that primarily affects elderly individuals, and is characterized by hallmark neuronal pathologies including extracellular amyloid-{beta} (A{beta}) plaque deposition, intracellular tau tangles, and neuronal death. However, recapitulating these age-associated neuronal pathologies in patient-derived neurons has remained a significant challenge, especially for late-onset AD (LOAD), the most common form of the disorder. Here, we applied the high efficiency microRNA-mediated direct neuronal reprogramming of fibroblasts from AD patients to generate cortical neurons in three-dimensional (3D) Matrigel and self-assembled neuronal spheroids. Our findings indicate that neurons and spheroids reprogrammed from both autosomal dominant AD (ADAD) and LOAD patients exhibited AD-like phenotypes linked to neurons, including extracellular A{beta} deposition, dystrophic neurites with hyperphosphorylated, K63-ubiquitin-positive, seed-competent tau, and spontaneous neuronal death in culture. Moreover, treatment with {beta}- or {gamma}-secretase inhibitors in LOAD patient-derived neurons and spheroids before A{beta} deposit formation significantly lowered A{beta} deposition, as well as tauopathy and neurodegeneration. However, the same treatment after the cells already formed A{beta} deposits only had a mild effect. Additionally, inhibiting the synthesis of age-associated retrotransposable elements (RTEs) by treating LOAD neurons and spheroids with the reverse transcriptase inhibitor, lamivudine, alleviated AD neuropathology. Overall, our results demonstrate that direct neuronal reprogramming of AD patient fibroblasts in a 3D environment can capture age-related neuropathology and reflect the interplay between A{beta} accumulation, tau dysregulation, and neuronal death. Moreover, miRNA-based 3D neuronal conversion provides a human-relevant AD model that can be used to identify compounds that can potentially ameliorate AD-associated pathologies and neurodegeneration.

neuroscience↗

bioRxiv2023

Endogenous pathology in tauopathy mice progresses via brain networks

Neurodegenerative tauopathies are hypothesized to propagate via brain networks. This is uncertain because we have lacked precise network resolution of pathology. We therefore developed whole-brain staining methods with anti-p-tau nanobodies and imaged in 3D PS19 tauopathy mice, which have pan-neuronal expression of full-length human tau containing the P301S mutation. We analyzed patterns of p-tau deposition across established brain networks at multiple ages, testing the relationship between structural connectivity and patterns of progressive pathology. We identified core regions with early tau deposition, and used network propagation modeling to determine the link between tau pathology and connectivity strength. We discovered a bias towards retrograde network-based propagation of tau. This novel approach establishes a fundamental role for brain networks in tau propagation, with implications for human disease. One-Sentence SummaryNovel whole brain imaging of p-tau deposition reveals retrograde-dominant network propagation in a tauopathy mouse model.

neuroscience↗

bioRxiv2023

Anti-tau antibodies targeting a conformation-dependent epitope selectively bind seeds

Neurodegenerative tauopathies are caused by transition of tau protein from a monomer to a toxic aggregate. They include Alzheimer disease (AD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Pick disease (PiD). We have previously proposed that tau monomer exists in two conformational ensembles: an inert form (Mi), which does not self-assemble; and seed-competent form (Ms), which self-assembles and templates ordered assembly growth. We proposed that cis/trans isomerization of tau at P301, the site of dominant disease-associated S/L mis-sense mutations, might underlie the transition of wild-type tau to a seed-competent state. Consequently, we created monoclonal antibodies using non-natural antigens consisting of fluorinated proline (P*) at the analogous P270 in R1, biased towards the trans-configuration at either the R1/R2 (TENLKHQP*GGGKVQIINKK) or R1/R3 (TENLKHQP*GGGKVQIVYK) interfaces. Two antibodies, MD2.2 and MD3.1 efficiently immunoprecipitated soluble seeds from AD and PSP, but not CBD or PiD. They stained brain samples of AD, PSP, and PiD, but not CBD. They did not immunoprecipitate, or immunostain tau from control brain. Creation of potent anti-seed antibodies based on the trans-proline epitope implicates local unfolding around P301 in pathogenesis. MD2.2 and MD3.1 may also be useful for therapy and diagnosis. SummaryTau protein undergoes conformational change to self-assemble and trigger neurodegeneration. We have proposed local unfolding events centered on P301 cis/trans isomerization, which expose amyloidogenic sequences. We used a non-natural peptide with a trans-proline to generate monoclonal antibodies that distinguish tau seeds from native tau in human brain. In addition to being important therapeutic and diagnostic leads, the activity of these antibodies supports structural studies implicating local conformational change in tau that underlies disease initiation.

neuroscience↗

bioRxiv2023

DnaJC7 specifically regulates tau seeding

Neurodegenerative tauopathies are caused by accumulation of toxic tau protein assemblies. This appears to involve template-based seeding events, whereby tau monomer changes conformation and is recruited to a growing aggregate. Several large families of chaperone proteins, including Hsp70s and J domain proteins (JDPs) cooperate to regulate the folding of intracellular proteins such as tau, but the factors that coordinate this activity are not well known. The JDP DnaJC7 binds tau and reduces its intracellular aggregation. However, it is unknown whether this is specific to DnaJC7 or if other JDPs might be similarly involved. We used proteomics within a cell model to determine that DnaJC7 co-purified with insoluble tau and colocalized with intracellular aggregates. We individually knocked out every possible JDP and tested the effect on intracellular aggregation and seeding. DnaJC7 knockout decreased aggregate clearance and increased intracellular tau seeding. This depended on the ability of the J domain (JD) of DnaJC7 to bind to Hsp70, as JD mutations that block binding to Hsp70 abrogated the protective activity. Disease-associated mutations in the JD and substrate binding site of DnaJC7 also abrogated its protective activity. DnaJC7 thus specifically regulates tau aggregation in cooperation with Hsp70.

molecular biology↗

bioRxiv2023

DNAJB8 oligomerization is mediated by an aromatic-rich motif that is dispensable for substrate activity

J-domain protein (JDP) molecular chaperones have emerged as central players that maintain a healthy proteome. The diverse members of the JDP family function as monomers/dimers and a small subset assemble into micron-sized oligomers. The oligomeric JDP members have eluded structural characterization due to their low-complexity, intrinsically disordered middle domains. This in turn, obscures the biological significance of these larger oligomers in protein folding processes. Here, we identified a short, aromatic motif within DNAJB8, that drives self-assembly through {nu}-{nu} stacking and determined its X-ray structure. We show that mutations in the motif disrupt DNAJB8 oligomerization in vitro and in cells. DNAJB8 variants that are unable to assemble bind to misfolded tau seeds more specifically and retain capacity to reduce protein aggregation in vitro and in cells. We propose a new model for DNAJB8 function in which the sequences in the low-complexity domains play distinct roles in assembly and substrate activity. HIGHLIGHTSDNAJB8 oligomerization is mediated by a short phenylalanine-based motif in the S/T domain Mutation of a single phenylalanine yields a monomeric form of DNAJB8 Monomeric DNABJ8 binds to an aggregation-prone substrate Monomeric DNAJB8 retains substrate aggregation prevention activity

biophysics↗

bioRxiv2022

FTD-tau S320F mutation stabilizes local structure and allosterically promotes amyloid motif-dependent aggregation

Amyloid deposition of the microtubule-associated protein tau is a unifying theme in a multitude of neurodegenerative diseases. Disease-associated missense mutations in tau are associated with frontotemporal dementia (FTD) and enhance tau aggregation propensity. However, the molecular mechanism of how mutations in tau promote tau assembly into amyloids remains obscure. There is a need to understand how tau folds into pathogenic conformations to cause disease. Here we describe the structural mechanism for how an FTD-tau S320F mutation drives spontaneous aggregation. We use recombinant protein and synthetic peptide systems, computational modeling, cross-linking mass spectrometry, and cell models to investigate the mechanism of spontaneous aggregation of the S320F FTD-tau mutant. We discover that the S320F mutation drives the stabilization of a local hydrophobic cluster which allosterically exposes the 306VQIVYK311 amyloid motif. We identify a suppressor mutation that reverses the S320F aggregation phenotype through the reduction of S320F-based hydrophobic clustering in vitro and in cells. Finally, we use structure-based computational design to engineer rapidly aggregating tau sequences by optimizing nonpolar clusters in proximity to the S320 site revealing a new principle that governs the regulation of tau aggregation. We uncover a mechanism for regulating aggregation that balances transient nonpolar contacts within local protective structures or in longer-range interactions that sequester amyloid motifs. The introduction of a pathogenic mutation redistributes these transient interactions to drive spontaneous aggregation. We anticipate deeper knowledge of this process will permit control of tau aggregation into discrete structural polymorphs to aid design of reagents that can detect disease-specific tau conformations.

biophysics↗