Surface expression of O‐specific lipopolysaccharide in <i>Escherichia coli</i> requires the function of the TolA protein
Bibliographic record
Abstract
We investigated the involvement of Tol proteins in the surface expression of lipopolysaccharide (LPS). tolQ, -R, -A and -B mutants of Escherichia coli K-12, which do not form a complete LPS-containing O antigen, were transformed with the O7+ cosmid pJHCV32. The tolA and tolQ mutants showed reduced O7 LPS expression compared with the respective isogenic parent strains. No changes in O7 LPS expression were found in the other tol mutants. The O7-deficient phenotype in the tolQ and tolA mutants was complemented with a plasmid encoding the tolQRA operon, but not with a similar plasmid containing a frameshift mutation inactivating tolA. Therefore, the reduction in O7 LPS was attributed to the lack of a functional tolA gene, caused either by a direct mutation of this gene or by a polar effect on tolA gene expression exerted by the tolQ mutation. Reduced surface expression of O7 LPS was not caused by changes in lipid A-core structure or downregulation of the O7 LPS promoter. However, an abnormal accumulation of radiolabelled mannose was detected in the plasma membrane. As mannose is a sugar unique to the O7 subunit, this result suggested the presence of accumulated O7 LPS biosynthesis intermediates. Attempts to construct a tolA mutant in the E. coli O7 wild-type strain VW187 were unsuccessful, suggesting that this mutation is lethal. In contrast, a polar tolQ mutation affecting tolA expression in VW187 caused slow growth rate and serum sensitivity in addition to reduced O7 LPS production. VW187 tolQ cells showed an elongated morphology and became permeable to the membrane-impermeable dye propidium iodide. All these phenotypes were corrected upon complementation with cloned tol genes but were not restored by complementation with the tolQRA operon containing the frameshift mutation in tolA. Our results demonstrate that the TolA protein plays a critical role in the surface expression of O antigen subunits by an as yet uncharacterized involvement in the processing of O antigen.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".