The Structure of the CS1 Pilus of Enterotoxigenic Escherichia coli Reveals Structural Polymorphism
Bibliographic record
Abstract
Enterotoxigenic Escherichia coli (ETEC) is a bacterial pathogen that causes diarrhea in children and travelers in developing countries. ETEC adheres to host epithelial cells in the small intestine via a variety of different pili. The CS1 pilus is a prototype for a family of related pili, including the CFA/I pili, present on ETEC and other Gram-negative bacterial pathogens. These pili are assembled by an outer membrane usher protein that catalyzes subunit polymerization via donor strand complementation, in which the N terminus of each incoming pilin subunit fits into a hydrophobic groove in the terminal subunit, completing a β-sheet in the Ig fold. Here we determined a crystal structure of the CS1 major pilin subunit, CooA, to a 1.6-Å resolution. CooA is a globular protein with an Ig fold and is similar in structure to the CFA/I major pilin CfaB. We determined three distinct negative-stain electron microscopic reconstructions of the CS1 pilus and generated pseudoatomic-resolution pilus structures using the CooA crystal structure. CS1 pili adopt multiple structural states with differences in subunit orientations and packing. We propose that the structural perturbations are accommodated by flexibility in the N-terminal donor strand of CooA and by plasticity in interactions between exposed flexible loops on adjacent subunits. Our results suggest that CS1 and other pili of this class are extensible filaments that can be stretched in response to mechanical stress encountered during colonization.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.000 | 0.000 |
| 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, unvalidatedMachine predicted; a candidate call from one teacher head, 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".