Recruitment of Both Uniform and Differential Binding Energy in Enzymatic Catalysis: Xylanases from Families 10 and 11
Notice bibliographique
Résumé
The contributions of enzyme-substrate hydrogen-binding interactions to catalysis by two different families of xylanases were evaluated through kinetic studies with two representative wild-type enzymes, Cellulomonas fimi xylanase (Cex) and Bacillus circulans xylanase (Bcx), on a series of monodeoxygenated and monodeoxyfluorinated p-nitrophenyl xylobioside substrates. Effects of substitution in the distal (-2 subsite) sugar on kcat/Km for Cex were moderately large (up to 2.9 kcal mol-1), with no effect seen on kcat. By contrast, substantial effects upon both kcat and kcat/Km were seen for substrates modified in the proximal (-1 subsite) sugar. Very similar results were obtained with Bcx. Kinetic analyses with a series of eight mutants of Cex in which active site residues interacting with the substrate were mutated yielded complementary insights. Again, interactions with the distal (-2) sugar were seen to contribute substantially to kcat/Km (up to 3.7 kcal mol-1), thus to the formation of the glycosyl-enzyme intermediate, but not to kcat, thus to the hydrolysis of the glycosyl-enzyme. Interactions with the proximal (-1) sugar are much more significant, contributing up to 6.7 kcal mol-1 to both kcat/Km and kcat. These results together indicate that interactions with the distal sugar maintain similar magnitudes in the transition states for glycosylation and deglycosylation as well as in the glycosyl-enzyme intermediate and can be referred to as "uniform binding interactions" in the parlance of Albery and Knowles (Albery, W. J., and Knowles, J. R. (1976) Biochemistry 15, 5631-5640). Interactions with the proximal sugar are considerably stronger at the deglycosylation transition state than in the intermediate, and fall into the category of differential binding interactions. This behavior likely has its origins in the changes in ring conformation of the proximal sugar but not of the distal sugar between the ground state and the reaction transition state. Correlation of these individual interaction energies with the hydrogen-bonding pattern seen in the glycosyl-enzyme intermediate allows for the assignment of hydrogen-bond strengths to each interaction, with good correlation between the two approaches. These findings are relevant to the discussion of remote binding effects upon enzymatic catalysis.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».