Nanomolar versus Millimolar Inhibition by Xylobiose-Derived Azasugars: Significant Differences between Two Structurally Distinct Xylanases
Bibliographic record
Abstract
The synthesis of xylobiose-derived nitrogen-containing inhibitors of xylanase is described starting with accessible precursors through efficient synthetic schemes. Four disaccharides were identified as powerful competitive inhibitors of the retaining family 10 xylanase, Cex, from Cellulomonas fimi, namely imidazole ( K i = 150 nM), lactam oxime ( K i = 370 nM), isofagomine ( K i = 130 nM), and deoxynojirimycin ( K i = 5800 nM) derivatives of xylobiose. By contrast, none of the compounds inhibited the family 11 xylanase, Bcx, from Bacillus circulans, to an appreciable extent. Two possible explanations are provided for the discrimination exhibited by the imidazole and the lactam oxime. One explanation relates to the different active site locations of the acid/base residue in the two enzymes: anti to the C1−O5 bond for the family 10 Cex and syn for the family 11 Bcx. The other explanation concerns proposed differences in the transition state conformation for the two enzymes: half-chair for Cex and boat for Bcx. The reasons for the difference in inhibition values between Cex and Bcx for the isofagomine and deoxynojirimycin derivatives are less clear-cut but may be ascribed to destabilizing steric and electrostatic interactions between the inhibitors and an essential tyrosine residue in the active site of Bcx.
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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 | 0.001 |
| 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".