Phosphatidylglycerol is the lipid donor for synthesis of phospholipid-linked enterobacterial common antigen
Bibliographic record
Abstract
ABSTRACT The gram-negative outer membrane (OM) is an asymmetric bilayer with phospholipids in its inner leaflet and mainly lipopolysaccharide (LPS) in its outer leaflet and is largely impermeable to many antibiotics. In Enterobacterales (e.g., Escherichia, Salmonella, Klebsiella, Yersinia ), the outer leaflet of the OM also contains phosphoglyceride-linked enterobacterial common antigen (ECA PG ). This molecule consists of the conserved ECA carbohydrate linked to diacylglycerol-phosphate (DAG-P) through a phosphodiester bond. ECA PG contributes to the OM permeability barrier and modeling suggests that it may alter the packing of LPS molecules in the OM. Here, we investigate, in Escherichia coli K-12, the reaction synthesizing ECA PG from ECA precursor linked to an isoprenoid carrier to identify the lipid donor that provides the DAG-P moiety to ECA PG . Through overexpression of phospholipid biosynthesis genes, we observed alterations expected to increase levels of phosphatidylglycerol (PG) increased synthesis of ECAPG, whereas alterations expected to decrease levels of PG decreased synthesis of ECA PG . We discovered depletion of PG levels in strains that could synthesize ECA PG , but not other forms of ECA, causes additional growth defects, likely due to the buildup of ECA precursor on the isoprenoid carrier inhibiting peptidoglycan biosynthesis. Our results demonstrate ECAPG can be synthesized in the absence of the other major phospholipids (phosphatidylethanolamine and cardiolipin). Overall, these results conclusively demonstrate PG is the lipid donor for the synthesis of ECA PG and provide a key insight into the reaction producing ECA PG . In addition, these results provide an interesting parallel to lipoprotein acylation, which also uses PG as its DAG donor. IMPORTANCE The outer membrane of gram-negative bacteria is a permeability barrier that prevents the entry of many antibiotics into the cell. However, the pathways responsible for outer membrane biogenesis are potential targets for small molecule development. Here, we investigate the synthesis of a form of enterobacterial common antigen (ECA), ECA PG , found in the outer membrane of Enterobacterales such as Escherichia, Salmonella, Klebsiella , and Yersinia . ECA PG consists of the conserved ECA carbohydrate unit linked to diacylglycerol-phosphate—ECA is the headgroup of a phospholipid. The details of the reaction forming this molecule from ECA linked to an isoprenoid carrier are unknown. We determined that the lipid donor that provides the phospholipid moiety to ECA PG is phosphatidylglycerol. Understanding the synthesis of outer membrane constituents such as ECA PG provides the opportunity for the development of molecules to increase outer membrane permeability, expanding the antibiotics available to treat gram-negative infections.
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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) | 0.001 | 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".