Effect of Neutral Pyridine Leaving Groups on the Mechanisms of Influenza Type A Viral Sialidase-Catalyzed and Spontaneous Hydrolysis Reactions of α-<scp>d</scp>-<i>N</i>-Acetylneuraminides
Bibliographic record
Abstract
A reagent panel, comprised of five pyridinium salts of α- d - N -acetylneuraminic acid, was synthesized and then used to probe enzymatic (α-sialidase) and nonenzymatic mechanisms of neuraminide hydrolysis. Spontaneous hydrolysis of the pyridinium salts proceeded via two independent pathways, where unassisted C−N bond cleavage was the rate-determining step. Cationic species (i.e., anomeric carboxylate protonated) displayed apparent p K a values in the range of 0.4−0.7. However, spontaneous hydrolyses of the cationic and zwitterionic species had similar β lg values of −1.22 ± 0.16 and −1.22 ± 0.07, respectively. The results, plus the activation parameters calculated from the hydrolysis of pyridinium α- d - N -acetylneuraminide (Δ H ⧧ = 112 ± 2 kJ mol - 1 and Δ S ⧧ = 28 ± 4 J mol - 1 K - 1 ), strongly suggest that the anomeric carboxylate does not assist in the departure of neutral pyridine leaving groups. Enzymatic hydrolysis was studied using an influenza viral α-sialidase (A/Tokyo/3/67) which was recombinantly expressed using a baculovirus/insect cell expression system. Sialidase protein was purified by a combination of density gradient centrifugation and gel filtration chromatography. Kinetic parameters for the enzymatic hydrolysis of the pyridinium salts were measured at 37 °C and at pH values of 6.0 and 9.5. The β lg values derived for k cat / K m and k cat were essentially zero, indicating that chemical transformations/events are not rate-determining. Rather, this observation is consistent with a model for α-sialidase-catalyzed hydrolyses (Guo, X.; Laver, W. G.; Vimr, E.; Sinnott, M. L. J. Am. Chem. Soc. 1994, 116, 5572) in which k cat / K m is determined by a conformational change of the first-formed Michaelis complex and k cat is determined by the virtual transition state made up of two separate conformational events.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| 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 | 0.001 |
| 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".