Assembly of the O Antigen in the Highly Pathogenic Escherichia Coli Serotype O104:H4
Bibliographic record
Abstract
Escherichia coli serotype O104:H4 (ECO104) is an intestinal pathogen that causes severe bloody diarrhea and hemolytic-uremic syndrome, which can lead to kidney failure and death. Lipopolysaccharides (LPS) are important virulence factors in Gram-negative bacteria and our goal is to understand the enzymes and mechanisms involved in the assembly of the outer O antigenic polysaccharides of the ECO104 LPS. The O antigen repeating unit of ECO104 has the structure [4-Galα1-4Neu5,7,9Ac3α2-3Galβ1-3GalNAcβ1-]n, which contains a mimic of the human sialyl-T-antigen found on certain types of cancer cells. Each monosaccharide subunit of the repeating structure is added sequentially by glycosyltransferases. These enzymes catalyze the transfer of a donor sugar from a nucleotide sugar onto a nucleophilic acceptor. Our aim was to biochemically characterize the second, third and fourth glycosyltransferases that synthesize the repeating unit of ECO104 by expressing the enzymes transgenically in non-pathogenic E. coli BL21, by purifying the enzymes and performing enzyme assays to determine substrate specificity, co-factor requirements, and enzyme kinetics, as well as creating single point mutations in the enzymes to identify key residues. The second enzyme, WbwC, a β1,3-Gal-transferase, has an absolute requirement for a diphosphate in the acceptor. Remarkably, the third enzyme, α2,3-sialyltransferase WbwA, and the fourth enzyme, α1,4-Gal-transferase WbwB, also have this requirement. This finding is unique in that glycosyltransferases further down the O antigen synthesis pathway usually do not require a diphosphate in the acceptor substrate. WbwB does not require any divalent metal ions for activity and several synthetic bis-imidazolium salts could inhibit the enzymes. This work provides insight into the biosynthesis of bacterial polysaccharides and identifies potential anti-bacterial targets and a strategy for vaccine synthesis.
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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) | 0.000 | 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".