Aspartate-107 and leucine-109 facilitate efficient coupling of glutamine hydrolysis to CTP synthesis by Escherichia coli CTP synthase
Bibliographic record
Abstract
CTP synthase catalyses the ATP-dependent formation of CTP from UTP using either NH(3) or L-glutamine as the nitrogen source. GTP is required as an allosteric effector to promote glutamine hydrolysis. In an attempt to identify nucleotide-binding sites, scanning alanine mutagenesis was conducted on a highly conserved region of amino acid sequence (residues 102-118) within the synthase domain of Escherichia coli CTP synthase. Mutant K102A CTP synthase exhibited wild-type activity with respect to NH(3) and glutamine; however, the R105A, D107A, L109A and G110A enzymes exhibited wild-type NH(3)-dependent activity and affinity for glutamine, but impaired glutamine-dependent CTP formation. The E103A, R104A and H118A enzymes exhibited no glutamine-dependent activity and were only partially active with NH(3). Although these observations were compatible with impaired activation by GTP, the apparent affinity of the D107A, L109A and G110A enzymes for GTP was reduced only 2-4-fold, suggesting that these residues do not play a significant role in GTP binding. In the presence of GTP, the k (cat) values for glutamine hydrolysis by the D107A and L109A enzymes were identical with that of wild-type CTP synthase. Overall, the kinetic properties of L109A CTP synthase were consistent with an uncoupling of glutamine hydrolysis from CTP formation that occurs because an NH(3) tunnel has its normal structure altered or fails to form. L109F CTP synthase was prepared to block totally the putative NH(3) tunnel; however, this enzyme's rate of glutamine-dependent CTP formation and glutaminase activity were both impaired. In addition, we observed that mutation of amino acids located between residues 102 and 118 in the synthase domain can affect the enzyme's glutaminase activity, suggesting that these residues interact with residues in the glutamine amide transfer domain because they are in close proximity or via a conformationally dependent signalling mechanism.
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 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".