Inhibition of Escherichia coli CTP synthase by glutamate γ-semialdehyde and the role of the allosteric effector GTP in glutamine hydrolysis
Bibliographic record
Abstract
Cytidine 5′-triphosphate synthase catalyses the ATP-dependent formation of CTP from UTP with either ammonia or glutamine as the source of nitrogen. When glutamine is the substrate, GTP is required as an allosteric effector to promote catalysis. Escherichia coli CTP synthase, overexpressed as a hexahistidine-tagged form, was purified to high specific activity with the use of metal-ion-affinity chromatography. Unfused CTP synthase, generated by the enzymic removal of the hexahistidine tag, displayed an activity identical with that of the purified native enzyme and was used to study the effect of GTP on the inhibition of enzymic activity by glutamate γ-semialdehyde. Glutamate γ-semialdehyde is expected to inhibit CTP synthase by reacting reversibly with the active-site Cys-379 to form an analogue of a tetrahedral intermediate in glutamine hydrolysis. Indeed, glutamate γ-semialdehyde is a potent linear mixed-type inhibitor of CTP synthase with respect to glutamine (Kis 0.16±0.03mM; Kii 0.4±0.1mM) and a competitive inhibitor with respect to ammonia (Ki 0.39±0.06mM) in the presence of GTP at pH8.0. The mutant enzyme (C379A), which is fully active with ammonia but has no glutamine-dependent activity, is not inhibited by glutamate γ-semialdehyde. Although glutamate γ-semialdehyde exists in solution primarily in its cyclic form, Δ1-pyrroline-5-carboxylate, the variation of inhibition with pH, and the weak inhibition by cyclic analogues of Δ1-pyrroline-5-carboxylate (l-proline, l-2-pyrrolidone and pyrrole-2-carboxylate) confirm that the rare open-chain aldehyde species causes the inhibition. When ammonia is employed as the substrate in the absence of GTP, the enzyme's affinity for glutamate γ-semialdehyde is decreased approx. 10-fold, indicating that the allosteric effector, GTP, functions by stabilizing the protein conformation that binds the tetrahedral intermediate(s) formed during glutamine hydrolysis.
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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 | 0.001 |
| 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".