SbnG, a Citrate Synthase in Staphylococcus aureus
Bibliographic record
Abstract
Background: Staphylococcus aureus contains a second, iron-regulated citrate synthase.Results: SbnG is a citrate synthase within the phosphoenolpyruvate/pyruvate superfamily.Conclusion: The structural similarity of the SbnG active site to TCA cycle citrate synthase active sites suggests convergent evolution.Significance: SbnG is defined as a new structural class of citrate synthase.In response to iron deprivation, Staphylococcus aureus produces staphyloferrin B, a citrate-containing siderophore that delivers iron back to the cell.This bacterium also possesses a second citrate synthase, SbnG, that is necessary for supplying citrate to the staphyloferrin B biosynthetic pathway.We present the structure of SbnG bound to the inhibitor calcium and an active site variant in complex with oxaloacetate.The overall fold of SbnG is structurally distinct from TCA cycle citrate synthases yet similar to metal-dependent class II aldolases.Phylogenetic analyses revealed that SbnG forms a separate clade with homologs from other siderophore biosynthetic gene clusters and is representative of a metal-independent subgroup in the phosphoenolpyruvate/pyruvate domain superfamily.A structural superposition of the SbnG active site to TCA cycle citrate synthases and site-directed mutagenesis suggests a case for convergent evolution toward a conserved catalytic mechanism for citrate production.
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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) | 0.000 | 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 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".