Structural basis of potassium activation in plant asparaginases
Bibliographic record
Abstract
l ‐asparaginases ( EC 3.5.1.1 ) play an important role in nitrogen mobilization in plants. Here, we investigated the biochemical and biophysical properties of potassium‐dependent (PvAspG1) and potassium‐independent (PvAspG‐T2) l ‐asparaginases from Phaseolus vulgaris . Our previous studies revealed that PvAspG1 requires potassium for catalytic activation and its crystal structure suggested that Ser‐118 in the activation loop plays a critical role in coordinating the metal cation. This amino acid residue is replaced by isoleucine in PvAspG‐T2. Reciprocal mutants of the enzymes were produced and the effect of the amino acid substitution on the kinetic parameters, allosteric effector binding, secondary structure conformation, and pH profile were studied. Introduction of the serine residue conferred potassium activation in PvAspG‐T2. Conversely, the PvAspG1‐S118I mutant could no longer be activated by potassium. PvAspG1 and the PvAspG‐T2‐I117S mutant had a similar half‐maximal effective concentration ( EC 50 ) value for potassium activation, between 0.1 and 0.3 m m . Potassium binding elicited a similar conformational change in PvAspG1 and PvAspG‐T2‐I117S, as studied by circular dichroism. However, no change in conformation was observed for PvAspG‐T2 and PvAspG1‐S118I. Analysis of kinetic parameters in function of pH indicated that potassium activation mediated by Ser‐118 influences the ionization of specific functional groups in the enzyme–substrate complex. Together, the results indicate that Ser‐118 of PvAspG1 is essential and sufficient for potassium activation in plant l ‐asparaginases. Enzyme l ‐Asparaginase ( EC 3.5.1.1 ).
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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) | 0.001 | 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".