The Klebsiella pneumoniae O2a Antigen Defines a Second Mechanism for O Antigen ATP-binding Cassette Transporters
Bibliographic record
Abstract
An ATP-binding cassette (ABC) transporter-dependent mechanism is responsible for the biosynthesis of polysaccharide O antigens in the lipopolysaccharides of many Gram-negative bacteria. In the Escherichia coli O9a prototype, addition of a non-reducing terminal modification regulates chain length. The terminal residue is an export signal recognized by the nucleotide-binding domain component of the cognate ABC transporter. The Klebsiella pneumoniae O2a antigen lacks a capping residue, and the corresponding nucleotide-binding protein does not contain a separate substrate-binding domain. Unlike the O9a transporter, the O2a transporter can export heterologous O antigens. Export of the O2a antigen is obligatorily coupled to chain elongation, and the O2a transporter is essential for establishing O antigen chain length. The E. coli O9a transporter operates after chain length has been determined. Furthermore biosynthesis and export can be uncoupled. O antigen chain length is a critical element in the ability of lipopolysaccharides to confer resistance to complement-mediated killing. This study establishes that two distinctly different approaches are available for the regulation of O antigen chain length and export via an ABC transporter.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".