A bifunctional ATPase drives tad pilus extension and retraction
Bibliographic record
Abstract
Abstract Molecular motors convert chemical energy directly into mechanical work 1 and are found in all domains of life 2 . These motors are critical to intracellular transport 3 , motility 4,5 , macromolecular protein assembly 3,6 , and many essential processes 7 . A wide-spread class of related bacterial motors drive the dynamic activity of extracellular fibers, such as type IV pili (T4P), that are extended and retracted using so-called secretion motor ATPases. Among these, the tight ad herence (tad) pili are critical for surface sensing, surface attachment, and biofilm formation 8–10 . How tad pili undergo dynamic cycles of extension and retraction 8 despite lacking a dedicated retraction motor ATPase has remained a mystery. Here we find that a bifunctional pilus motor ATPase, CpaF, drives both activities through ATP hydrolysis. Specifically, we show that mutations within the ATP hydrolysis active site of Caulobacter crescentus CpaF result in a correlated reduction in the rates of extension and retraction. Moreover, a decrease in the rate of ATP hydrolysis directly scales with a decrease in the force of retraction and reduced dynamics in these CpaF mutants. This mechanism of motor protein bifunctionality extends to another genus of tad-bearing bacteria. In contrast, the T4aP subclass of pili possess dedicated extension and retraction motor ATPase paralogs. We show that these processes are uncoupled using a slow ATP hydrolysis mutation in the extension ATPase of competence T4aP of Vibrio cholerae that decreases the rate of extension but has no effect on the rate of retraction. Thus, a single motor ATPase is able to drive the bidirectional processes of pilus fiber extension and retraction.
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How this classification was reachedexpand
Direct model labels (unvalidated)
Per-model category and study-design labels from the labeling rounds. They are machine output, unvalidated, and the disagreement between models ships as data. No study design here is MEDLINE-validated yet.
| Model arm | Categories | Study design | Confidence |
|---|---|---|---|
| gemma | no category Domain: not available · Genre: Empirical About the Canadian research system: no · About a Canadian topic: no | Bench or experimental | low |
| gpt | no category Domain: not available · Genre: Empirical About the Canadian research system: no · About a Canadian topic: no | Bench or experimental | high |
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) | 0.001 | 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 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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, unvalidatedLabeled directly by 2 models reading the full record.
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".