Exploring the Substrate Specificity of a Mycobacterial Polyprenol Monophosphomannose‐Dependent α‐(1→6)‐Mannosyltransferase
Bibliographic record
Abstract
A series of synthetic alpha-(1-->6)-linked octyl mannopyranoside oligomers was evaluated as potential acceptors of a polyprenol monophosphomannose-dependent alpha-(1-->6)-mannosyltransferase that is involved in the biosynthesis of the mannan core of mycobacterial lipoarabinomannan. Initial evaluation demonstrated that the enzyme recognizes di-, tri- and tetramannosides (5, 6 and 7) as substrates with different activities. While the highest mannosyltransferase activities were observed when the di- and trisaccharide were used as substrates, diminished enzymatic activity was seen with the tetramannoside. As octyl alpha-D-mannopyranosyl-(1-->6)-alpha-D-mannopyranoside (5) appears to be the minimum structural element required for mannosyltransferase catalysis, a panel of methoxy and deoxy disaccharide analogues (8-21) were used to probe the substrate specificity of the enzyme further. In terms of the steric requirements at the active site, the enzyme does not recognize either C2'- and C2-methoxy analogues as substrates, a result that suggests that the alpha-(1-->2)-mannopyranosyl branches, which are present in the mannan core of LAM must be added on a larger alpha-(1-->6)-oligomannan intermediate. In contrast, the presence of a methoxy functionality at the C3', C3, C4' and C4 positions are somewhat tolerated by the enzyme, although diminished enzyme activities were observed with the C4'- and C4-methoxy analogues. Moreover, the 2'- and 4-hydroxyl groups appear not to be critical for substrate binding at the active site, as both 2'- and 4-deoxy analogues are substrates for the enzyme. In contrast, replacement of the hydroxyl groups at other positions essentially abolished enzymatic activity. Further kinetic characterization of the enzyme by using the effective acceptor substrates gave apparent K(M) values ranging from 111 to 437 microM, which are within two-fold higher or lower than that for the parent dimannoside (5). Although the K(M) values indicate that the enzyme binds those acceptors with comparable affinities, the C4'-methoxy analogue (12) turns over more slowly than the others, as indicated by the apparent V(max) values.
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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".