Sugar-nucleotide-binding and autoglycosylating polypeptide(s) from nasturtium fruit: biochemical capacities and potential functions
Bibliographic record
Abstract
Polypeptide assemblies cross-linked by S-S bonds (molecular mass > 200 kDa) and single polypeptides folded with internal S-S cross-links (< 41 kDa) have been detected by SDS/PAGE in particulate membranes and soluble extracts of developing cotyledons of nasturtium (Tropaeolum majus L.). When first prepared from fruit homogenates, these polypeptides were found to bind reversibly to UDP-Gal (labelled with [14C]Gal or [3H]uridine), and to co-precipitate specifically with added xyloglucan from solutions made with 67% ethanol. Initially, the bound UDP-[14C]Gal could be replaced (bumped) by adding excess UDP, or exchanged (chased) with UDP-Gal, -Glc, -Man or -Xyl. However, this capacity for turnover was lost during incubation in reaction media, or during SDS/PAGE under reducing conditions, even as the glycone moiety was conserved by autoglycosylation to form a stable 41 kDa polypeptide. Polyclonal antibodies raised to a similar product purified from Arabidopsis bound to all the labelled nasturtium polypeptides in immunoblotting tests. The antibodies also inhibited the binding of nasturtium polypeptides to UDP-Gal, the uptake of UDP-[14C]Gal into intact nasturtium membrane vesicles and the incorporation of [14C]Gal into nascent xyloglucan within these vesicles. This is the first direct evidence that these polypeptides facilitate the channelling of UDP-activated sugars from the cytoplasm through Golgi vesicle membranes to lumenal sites, where they can be used as substrates for glycosyltransferases to synthesize products such as xyloglucan.
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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) | 0.001 | 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".