Structure of a novel lipid A obtained from the lipopolysaccharide of <i>Caulobacter crescentus</i>
Bibliographic record
Abstract
Caulobacter crescentus CB15 is a dimorphic bacterium that is best known as a prokaryotic model for cell development. However, it is also being exploited in biotechnology, where the crystalline surface (S-layer) protein secretion system has been adapted for heterologous protein display or secretion. Because the S-layer attaches to the cell surface via lipopolysaccharide (LPS) and since the LPS represents a potential endotoxin contaminant of recombinant proteins, the lipid A component was examined in detail. LPS was acid hydrolyzed to obtain crude lipid A, which was methylated and purified by HPLC. HPLC peak fractions were analyzed by mass spectrometry and nuclear magnetic resonance spectroscopy. The structure of the major lipid A of C. crescentus comprised the tetrasaccharide backbone alpha-D-GalpA-(1-->4)-beta-D-DAG-(1-->6)-alpha-D-DAG-(1-->1)-alpha-D-GalpA substituted with six fatty acids, and a molecular mass of 1875 (GalpA, galactopyranuronic acid; DAG, 2,3-diamino-2,3-dideoxyglucopyranose). No phosphate residues were detected. The major lipid A component had 12:0[3-O[Delta(5)-12:1(3-OH)]] and 12:0[3-O(Delta(5)-12:1)] fatty acyl chains at either the 3'- or the 2' positions of the distal subunit DAG B, and 12:0(3-OH) and 12:0[3,6-(OH)( 2)] fatty acyl chains at 3- and 2- positions of the reducing end subunit DAG A, respectively. In addition, several other variations in the structure were observed. The LPS was evaluated for TNF-alpha inducing activity and consistent with its unusual lipid A structure (relative to that of enteric bacteria), the activity was reduced by greater than 100-fold as compared to Escherichia coli ReLPS. This and other evidence suggests the potential application of this lipid A as a vaccine adjuvant or the suitability of Caulobacter displaying antigens for formulation of whole cell vaccines.
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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 | 0.001 |
| 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".