<i>O</i>-GlcNAcase Catalyzes Cleavage of Thioglycosides without General Acid Catalysis
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Bibliographic record
Abstract
O-GlcNAcase catalyzes the removal of N-acetylglucosamine residues from serine and threonine residues of post-translationally modified proteins using a catalytic mechanism involving substrate-assisted catalysis and general acid/base catalysis. Since thioglycosides are widely perceived as resistant to hydrolysis by glycosidases, it was surprising to find that O-GlcNAcase also catalyzes the efficient hydrolysis of S-glycosides. Brønsted analyses and pH-activity studies of the O-GlcNAcase-catalyzed hydrolysis of a series of aryl S- and O-glycosides reveal that O-GlcNAcase effects hydrolysis of thioglycosides without the assistance of general acid catalysis. alpha-Deuterium kinetic isotope effects for O- and S-glycosides, as well as Taft-like analyses using N-fluoroacetyl-beta-glycosides, suggest that O-GlcNAcase accomplishes hydrolysis of thioglycosides by stabilizing late transition states. For S-glycosides this transition state shows greater nucleophilic participation from the 2-acetamido group than for O-glycosides. The rate constants governing the O-GlcNAcase-catalyzed hydrolysis of O- and S-glycosides as compared to those previously determined for the spontaneous hydrolysis of structurally similar O,O- and O,S-acetals show a similar ratio. O-GlcNAcase therefore demonstrates similar catalytic proficiency toward both O- and S-glycosides. We conclude that O-GlcNAcase is a bifunctional catalyst capable of efficiently cleaving thioglycosides without general acid catalysis, an observation that may have biological implications.
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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) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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 it