Lipid Trafficking Controls Endotoxin Acylation in Outer Membranes of Escherichia coli
Why this work is in the frame
A frame that forgets how it found something cannot be audited. These are the routes that admitted this work.
Bibliographic record
Abstract
The biogenesis of biological membranes hinges on the coordinated trafficking of membrane lipids between distinct cellular compartments. The bacterial outer membrane enzyme PagP confers resistance to host immune defenses by transferring a palmitate chain from a phospholipid to the lipid A (endotoxin) component of lipopolysaccharide. PagP is an eight-stranded antiparallel beta-barrel, preceded by an N-terminal amphipathic alpha-helix. The active site is localized inside the beta-barrel and is aligned with the lipopolysaccharide-containing outer leaflet, but the phospholipid substrates are normally restricted to the inner leaflet of the asymmetric outer membrane. We examined the possibility that PagP activity in vivo depends on the aberrant migration of phospholipids into the outer leaflet. We find that brief addition to Escherichia coli cultures of millimolar EDTA, which is reported to replace a fraction of lipopolysaccharide with phospholipids, rapidly induces palmitoylation of lipid A. Although expression of the E. coli pagP gene is induced during Mg2+ limitation by the phoPQ two-component signal transduction pathway, EDTA-induced lipid A palmitoylation occurs more rapidly than pagP induction and is independent of de novo protein synthesis. EDTA-induced lipid A palmitoylation requires functional MsbA, an essential ATP-binding cassette transporter needed for lipid transport to the outer membrane. A potential role for the PagP alpha-helix in phospholipid translocation to the outer leaflet was excluded by showing that alpha-helix deletions are active in vivo. Neither EDTA nor Mg(2+)-EDTA stimulate PagP activity in vitro. These findings suggest that PagP remains dormant in outer membranes until Mg2+ limitation promotes the migration of phospholipids into the outer leaflet.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 it