Two Nucleophilic Mutants of the <i>Micromonospora viridifaciens</i> Sialidase Operate with Retention of Configuration by Two Different Mechanisms
Why this work is in the frame
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Bibliographic record
Abstract
Mutants of the Micromonospora viridifaciens sialidase, Y370E and Y370F, are catalytically active retaining enzymes that operate by different mechanisms. Previous substitutions with smaller amino acids, including Y370D, yielded inverting sialidases. At least one water molecule can fit into the active-site cavity of this mutant and act as a nucleophile from the face opposite the leaving group (Biochemistry 2003, 42, 12 682). Thus, addition of a CH(2) unit (Asp versus Glu) changes the mechanism from inversion back to retention of configuration. Based on Brønsted beta(lg) values, it is proposed that the Y370E mutant reacts by a double-displacement mechanism (beta(lg) on k(cat)/K(m) -0.36+/-0.04) with Glu370 acting as the nucleophile. However, the Y370F mutant (beta(lg) on k(cat)/K(m) -0.79+/-0.12) reacts via a dissociative transition state. The crystal structure of the Y370F mutant complexed with 2-deoxy-2,3-dehydro-N-acetylneuraminic acid shows no significant active-site perturbation relative to the wild-type enzyme.
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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 | 0.000 |
| 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 it