Structure of the ciliary tip central pair reveals the unique role of the microtubule-seam binding protein SPEF1
Bibliographic record
Abstract
Abstract Motile cilia are unique organelles with the ability to autonomously move. Force generated by beating cilia propels cells and moves fluids. The ciliary skeleton is made of peripheral doublet microtubules and a central pair (CP) with a distinct structure at the tip. In this study, we present a high-resolution structure of the CP in the ciliary tip of the ciliate Tetrahymena thermophila and identify several tip proteins that bind and form unique patterns on both microtubules of the tip CP. Two of those proteins that contain tubulin polymerization-promoting protein (TPPP)-like domains, TLP1 and TLP2, bind to high curvature regions of the microtubule. TLP2, which contains two TPPP-like domains, is an unusually long protein that wraps laterally around half a microtubule and forms the bridge between the two microtubules. Moreover, we found that the conserved protein SPEF1 binds to both microtubule seams. In vitro , human SPEF1 not only binds to the microtubule seam but also crosslinks two parallel microtubules. Single-molecule microtubule dynamics assays indicate that SPEF1 stabilizes microtubules in vitro . Together, these data show that the proteins in the tip CP maintain stable microtubule structure and probably play important roles in maintaining the integrity of the axoneme.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".