Revisiting the Specificity of an α‐(1→4)‐Mannosyltransferase Involved in Mycobacterial Methylmannose Polysaccharide Biosynthesis
Bibliographic record
Abstract
In order to evaluate the proposed biosynthetic pathway for the methylmannose (MMPs) polysaccharides produced by mycobacteria, two homologous series of synthetic α-(1→4)-linked 3-O-methyl-mannopyranosides, one terminated at the non-reducing end by a free mannopyranose residue (unmethylated oligosaccharides; OS) and the other terminated by a 3-O-methyl-mannopyranose residue (methylated OS), were prepared and evaluated as potential acceptors of an α-(1→4)-mannosyltransferase. Using a mycobacterial membrane preparation as the source of the transferase, it was found that unmethylated OS are better substrates for the enzyme compared to the methylated OS of the same length. These results are inconsistent with the proposed MMP biosynthetic pathway, which suggests only methylated OS are acceptors of this transferase. To confirm that the observed activity arose from the desired α-(1→4)-mannosyltransferase, as opposed to other mannosyltransferases present in the membrane preparation, the products resulting from tetrasaccharides 4 (unmethylated OS) and 9 (methylated OS), which only differ in the terminal residue, were further analyzed. MALDI-MS, exo-glycosidase digestion and (1) H NMR spectroscopy were used to evaluate the structures of these reaction products. These experiments revealed that the enzymatic products of both 4 and 9 contain only α-(1→4)-linked mannose residues, confirming the activity of the α-(1→4)-mannosyltransferase. This supports the finding that both methylated and unmethylated OS are acceptors of the enzyme. It was also demonstrated that a homologous series of oligosaccharides with different number of mannose residues were formed from both 4 and 9, as opposed to a single reaction product. These results, again, challenge the previously proposed MMP biosynthetic pathway involving alternating methylation and mannosylation reactions.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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 teacher head, 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".