<i>Staphylococcus aureus</i> Cap5O Has UDP-ManNAc Dehydrogenase Activity and Is Essential for Capsule Expression
Bibliographic record
Abstract
The Staphylococcus aureus serotype 5 capsular polysaccharide (CP5) has a repeating unit composed of (-->4)-3-O-acetyl-beta-D-ManNAcA-(1-->4)-alpha-L-FucNAc (1-->3)-beta-D-FucNAc-(1-->)(n). Sixteen chromosomal genes (cap5A through cap5P) are involved in the synthesis of CP5. We recently demonstrated that Cap5P, a 2-epimerase, catalyzes the conversion of UDP-N-acetyl glucosamine (UDP-GlcNAc) to UDP-N-acetylmannosamine (UDP-ManNAc). In this study, we show that UDP-ManNAc is oxidized to UDP-N-acetylmannosaminuronic acid (UDP-ManNAcA) by a UDP-ManNAc dehydrogenase encoded by S. aureus cap5O. We expressed Cap5O in Escherichia coli and purified the recombinant protein. The UDP-ManNAc dehydrogenase activity of purified Cap5O was assessed by incubating Cap5P and UDP-GlcNAc (to produce UDP-ManNAc), together with Cap5O, NAD(+), and a reducing agent. Enzymatic activity was quantitated indirectly by measuring the increase in absorbance at 340 nm resulting from NADH formation. The product of the reaction was confirmed as UDP-ManNAcA by gas chromatography-mass spectroscopy. A cap5O mutation, created by deletion of 727 bp in the 5' end of the gene, was introduced by allelic replacement into S. aureus Reynolds, rendering it CP5 negative. Mice inoculated intravenously or subcutaneously with the wild-type strain Reynolds had greater numbers of S. aureus recovered from their kidneys (P = 0.019) or their subcutaneous abscesses (P = 0.0018), respectively, than did animals inoculated with the cap5O mutant. The results of this study indicate that S. aureus cap5O is essential for capsule production and that capsule promotes staphylococcal virulence in mouse models of abscess formation.
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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 | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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".