Identification of a novel N-linked glycan on the archaellins and S-layer protein of the thermophilic methanogen, Methanothermococcus thermolithotrophicus
Bibliographic record
Abstract
Motility in archaea is facilitated by a unique structure termed the archaellum. N -Glycosylation of the major structural proteins (archaellins) is important for their subsequent incorporation into the archaellum filament. The identity of some of these N -glycans has been determined, but archaea exhibit extensive variation in their glycans, meaning that further investigations can shed light not only on the specific details of archaellin structure and function, but also on archaeal glycobiology in general. Here we describe the structural characterization of the N -linked glycan modifications on the archaellins and S-layer protein of Methanothermococcus thermolithotrophicus , a methanogen that grows optimally at 65 °C. SDS-PAGE and MS analysis revealed that the sheared archaella are composed principally of two of the four predicted archaellins, FlaB1 and FlaB3, which are modified with a branched, heptameric glycan at all N -linked sequons except for the site closest to the N termini of both proteins. NMR analysis of the purified glycan determined the structure to be α-d- glycero -d- manno -Hep3OMe6OMe-(1–3)-[α-GalNAcA3OMe-(1–2)-]-β-Man-(1–4)-[β-GalA3OMe4OAc6CMe-(1–4)-α-GalA-(1–2)-]-α-GalAN-(1–3)-β-GalNAc-Asn. A detailed investigation by hydrophilic interaction liquid ion chromatography–MS discovered the presence of several, less abundant glycan variants, related to but distinct from the main heptameric glycan. In addition, we confirmed that the S-layer protein is modified with the same heptameric glycan, suggesting a common N -glycosylation pathway. The M. thermolithotrophicus archaellin N -linked glycan is larger and more complex than those previously identified on the archaellins of related mesophilic methanogens, Methanococcus voltae and Methanococcus maripaludis . This could indicate that the nature of the glycan modification may have a role to play in maintaining stability at elevated temperatures.
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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".