Bacterial and Viral Sialidases: Contribution of the Conserved Active Site Glutamate to Catalysis
Bibliographic record
Abstract
Mutagenesis of the conserved glutamic acid of influenza type A (E277) and Micromonospora viridifaciens (E260) sialidases was performed to probe the contribution of this strictly conserved residue to catalysis. Kinetic studies of the E260D and E260C M. viridifaciens mutant enzymes reveal that the overall mechanism of action has not changed. That is, the mutants are retaining sialidases in which glycosylation and deglycosylation are rate-limiting for k(cat)/K(m) and k(cat), respectively. The solvent kinetic isotope effect and proton inventory on k(cat) for the E260C mutant sialidase provide strong evidence that the newly installed cysteine residue provides little catalytic acceleration. The results are consistent with the conserved aspartic acid residue (D92) becoming the key general acid/base residue in the catalytic cycle. In addition, the E277D mutant influenza type A sialidase is catalytically active toward 4-nitrophenyl α-D-sialoside, although no measurable hydrolysis of natural substrates was observed. Thus, mutating the glutamate residue (E277) to an aspartate increases the activation free energy of hydrolysis for natural substrates by >22 kJ/mol.
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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".