Formation of the β-sheet at the extracellular opening of the intimin β-barrel domain is necessary for stability and efficient passenger secretion
Bibliographic record
Abstract
Abstract Attaching and effacing pathogens, such as enteropathogenic and enterohaemorrhagic E. coli , rely on an adhesin, intimin, for attachment to enterocytes and downstream effects leading to actin pedestal formation. Intimin belongs to the inverse autotransporter family (type 5e secretion systems), which secrete the extracellular adhesive domain or passenger via a hairpin intermediate. While many of the next steps in secretion are now understood, how the hairpin initially forms is not known. We sought to investigate this by making point mutations at several positions in the β-barrel domain of intimin, as this domain forms at least part of the secretion pore. We made the mutations in a wild-type background and in a stalled intermediate caught in the hairpin conformation, which allowed us to uncouple passenger secretion from hairpin formation. Surprisingly, most of the point mutations did not have an appreciable effect on hairpin formation or passenger secretion, and larger changes such as replacing the entire linker region with a flexible glycine-serine stretch showed only a modest reduction in passenger secretion. By contrast, mutations affecting a small β-sheet at the extracellular face of the intimin β-barrel between two extracellular loops and the C-terminus of the linker had a more pronounced effect on secretion, and abolishing this β-sheet prevented hairpin formation and led to complete loss of the wild-type protein. Our results show that the intimin β-barrel is remarkably tolerant to changes and that the β-sheet on the extracellular side of this domain plays a central role in passenger secretion and protein stability.
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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 | 0.000 | 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 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".