Purification and Characterization of WaaP from Escherichia coli, a Lipopolysaccharide Kinase Essential for Outer Membrane Stability
Bibliographic record
Abstract
In Escherichia coli, Salmonella enterica, and Pseudomonas aeruginosa, the waaP (rfaP) gene product is required for the addition of phosphate to O-4 of the first heptose residue of the lipopolysaccharide (LPS) inner core region. This phosphate substitution is particularly important to the biology of these bacteria; it has previously been shown that WaaP is necessary for resistance to hydrophobic and polycationic antimicrobials in E. coli and that it is required for virulence in invasive strains of S. enterica. WaaP function is also known to be essential for the viability of P. aeruginosa. The predicted WaaP protein shows low levels of similarity (10-15% identity) to eukaryotic protein kinases, but its kinase activity has never been tested. Here we report the purification of WaaP and the reconstitution of its enzymatic activity in vitro. The purified enzyme catalyzes the incorporation of 33P from [gamma-33P]ATP into acceptor LPS purified from a defined E. coli waaP mutant. Enzymatic activity is dependent upon the presence of Mg2+ and is maximal from pH 8.0 to 9.0. The apparent Km (determined at saturating concentrations of the second substrate) is 0.13 mm for ATP and 76 microm for LPS. These data are the first proof that WaaP is indeed an LPS kinase. Further, site-directed mutagenesis of a predicted catalytic residue suggests that WaaP shares a common mechanism of action with eukaryotic protein kinases.
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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".