Synthetic UDP-galactofuranose analogs reveal critical enzyme–substrate interactions in GlfT2-catalyzed mycobacterial galactan assembly
Bibliographic record
Abstract
Mycobacterial cell wall galactan, composed of alternating β-(1→5) and β-(1→6) galactofuranosyl residues, is assembled by the action of two bifunctional galactofuranosyltransferases, GlfT1 and GlfT2, which use UDP-galactofuranose (UDP-Galf) as the donor substrate. Kinetic analysis of synthetic UDP-Galf analogs identified critical interactions involved in donor substrate recognition by GlfT2, a processive polymerizing glycosyltransferase. Testing of methylated UDP-Galf analogs showed the donor substrate-binding pocket is sterically crowded. Evaluation of deoxy UDP-Galf analogs revealed that the C-6 hydroxyl group is not essential for substrate activity, and that interactions with the UDP-Galf C-3 hydroxyl group orient the substrate for turnover but appears to play no role in substrate recognition, making the 3-deoxy-analog a moderate competitive inhibitor of the enzyme. Moreover, the addition of a Galf residue deoxygenated at C-5 or C-6, or an l-arabinofuranose residue, to the growing galactan chain resulted in "dead end" reaction products, which no longer act as an acceptor for the enzyme. This finding shows dual recognition of both the terminal C-5 and C-6 hydroxyl groups of the acceptor substrate are required for GlfT2 activity, which is consistent with a recent model developed based upon a crystal structure of the enzyme. These observations provide insight into specific protein-carbohydrate interactions in the GlfT2 active site and may facilitate the design of future inhibitors.
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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) | 0.001 | 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".