Structural heterogeneity of CTE Type I tau filaments with an interface-shifted polymorph
molecular biology
Quick verdict
Public CTE cryo-EM reanalysis finds an interface-shifted Type I-like tau polymorph (2.96 Å) coexisting with Type I in single fibrils; single-dataset evidence.
Summary
The authors reprocessed publicly archived cryo-EM data of brain-derived CTE tau filaments (EMPIAR-10313; 5,303 micrographs, ~203,000 deposited Type I coordinates) in RELION 5.0 to test whether the CTE Type I protofilament interface — which their prior work showed can be chemically shifted in vacuolar tauopathy VT Ia — also admits alternative packing in CTE itself. Four-class 3D classification separated a dominant CTE Type I population (150,228 particles) from a 22% minor class termed CTE Type I-like, refined with C1 symmetry to 2.78 and 2.96 Å at identical helical parameters (179.4° twist, 2.37 Å rise). Both models span residues V306–R379 with the same protofilament fold; the difference is lateral packing — the interface shifts from a G323–H329-centered network of six hydrogen bonds per cross-β rung to a G323–N327-centered network of four, with 21% less buried surface (874 vs 1,108 Ų). Back-projecting particle-state assignments onto micrographs identified 2,337 high-coverage fibrils: 43.0% pure Type I, 4.5% pure Type I-like, 52.5% mixed, with 417 fibrils showing transitions flanked by at least five consecutively spaced same-state segments per side. Main limitations: everything derives from one public dataset; state labels rest on classification against a heterologous VT IV reference without per-particle confidence thresholds or a misclassification null model; and overlapping helical segments make adjacent assignments non-independent (acknowledged but unquantified). Maps and models are deposited; the analysis code's Zenodo DOI is still reserved.
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Assessment at a glance
4
risk flags identified
● high 0
● medium 2
● low 2
5 strengths · 5 weaknesses · 5 author questions
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Key claims under review
- A previously unreported brain-derived CTE tau filament structure, CTE Type I-like, retains the CTE Type I protofilament fold (residues V306–R379) but shifts the inter-protofilament interface from a G323–H329-centered network of six hydrogen bonds per cross-β rung to a G323–N327-centered network of four, with 21% less buried surface (874 vs 1,108 Ų), refined at 2.96 Å versus 2.78 Å for Type I.
- Back-projection of particle state assignments onto micrographs shows the two packing states occupy locally contiguous regions within individual fibrils: of 2,337 high-coverage fibrils, 52.5% are mixed and 417 (17.8% of the cohort) contain locally supported transitions flanked by at least five consecutively spaced same-state particles on each side.
- Pure CTE Type I-like fibrils (104; 4.5%) exist, indicating this packing state is maintained during fibril elongation rather than occurring only at transition sites.
- The absence of salt-bridge electrostatics at the CTE Type I interface may permit multiple packing geometries, consistent with amyloid mechanical anisotropy and observed protofilament sliding in time-resolved cryo-EM of recombinant tau.
Strengths
New brain-derived structure extracted from existing public data
A previously unreported CTE filament (2.96 Å, EMD-78522/PDB 37VY) was resolved purely by reprocessing EMPIAR-10313, and the result is hypothesis-driven: the same fold-with-shifted-interface motif the authors observed for VT Ia after ubistatin B treatment (ref 3) is shown to occur natively in CTE Type I, giving the reanalysis a coherent rationale rather than an opportunistic one.
Quantitative, symmetrically computed interface comparison
Interface differences are measured, not merely visualized: hydrogen bonds per cross-β rung counted with identical relaxed criteria for both structures (0.4 Å / 20° tolerances; 6 vs 4 per rung), buried inter-protofilament SASA computed on matched seven-rung models (1,108 vs 874 Ų, 21% smaller), plus MolProbity 2.21/2.20, no Ramachandran outliers, and half-map cross-validation supporting both models.
Conservative transition definition for the fibril-level claim
Fully reported workflow with deposition
Careful positioning against the closest prior mixed-filament report
Weaknesses
Single dataset, single case
No null model for classification-driven artifacts
Pooling of three Type I classes is unjustified
Reference and prior choices could shape the class separation
Selection effects on fibril composition uncharacterized
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Frequently asked questions
What is the new CTE Type I-like tau filament structure?
It is a cryo-EM structure of brain-derived chronic traumatic encephalopathy (CTE) tau filaments that keeps the same protofilament fold as the known CTE Type I filament but changes how the two protofilaments pack against each other. The interface shifts from a G323–H329-centered network with six hydrogen bonds per rung to a G323–N327-centered network with four, and about 21% less buried surface area. It was resolved at 2.96 Å by reprocessing previously published microscope data (EMPIAR-10313).
Did the authors collect new brain tissue or new cryo-EM data for this study?
No. The study is a reanalysis of publicly archived data (EMPIAR-10313) originally collected by Falcon and colleagues for the 2019 CTE tau filament structure. The authors reprocessed roughly 200,000 filament image segments in RELION 5.0 and deposited their new maps and models as EMD-78521/78522 and PDB 37VX/37VY.
What does it mean that the two tau packing states coexist within a single fibril?
By tracing which of the two structures each image segment was assigned to back onto its original position along the fibril, the authors found that many individual fibrils contain a stretch of CTE Type I packing followed by a stretch of the shifted Type I-like packing. About 53% of well-covered fibrils were mixed, and in 417 fibrils each switch was flanked by at least five consecutive same-state segments on both sides, arguing the transitions are locally real rather than classification noise.
Why does a shifted protofilament interface matter for CTE research?
Tau filaments propagate as structurally distinct strains, and inter-protofilament packing is what defines a filament type. Showing that a single fibril can switch packing states along its length adds a level of polymorphism beyond the discrete filament types catalogued so far, which may be relevant to how tau strains replicate and convert, and to drugs designed to target the filament interface.
About this review
This is an AI-generated preliminary review by Evolve.Pub, produced from the openly available text of the paper. It is not peer review and does not represent the authors' views. The canonical record of the paper is at the publisher link above.
- Figures were not analyzable (only legends and rasterized figure text were extracted); map quality, interface geometry, and micrograph overlays are judged from the text narrative and deposited accession IDs alone.
- Table S1 (model-refinement and validation statistics) was referenced but not included in the extracted text; validation numbers cited here come from the Results narrative.
- Supplementary material beyond the Fig. S1 references was unavailable.
- The extraction contained duplicated bioRxiv license boilerplate between paragraphs but appeared otherwise complete from title through references.
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