The Lectin Chaperone Calnexin Utilizes Polypeptide-based Interactions to Associate with Many of Its Substrates in Vivo
Bibliographic record
Abstract
Calnexin and calreticulin are molecular chaperones of the endoplasmic reticulum that bind to newly synthesized glycoproteins in part through a lectin site specific for monoglucosylated (Glc(1)Man(7-9)GlcNAc(2)) oligosaccharides. In addition to this lectin-oligosaccharide interaction, in vitro studies have demonstrated that calnexin and calreticulin can bind to polypeptide segments of both glycosylated and nonglycosylated proteins. However, the in vivo relevance of this latter interaction has been questioned. We examined whether polypeptide-based interactions occur between calnexin and its substrates in vivo using the glucosidase inhibitor castanospermine or glucosidase-deficient cells to prevent the formation of monoglucosylated oligosaccharides. We show that if care is taken to preserve weak interactions, the block in lectin-oligosaccharide binding leads to the loss of some calnexin-substrate complexes, but many others remain readily detectable. Furthermore, we demonstrate that calnexin is capable of associating in vivo with a substrate that completely lacks Asn-linked oligosaccharides. The binding of calnexin to proteins that lack monoglucosylated oligosaccharides could not be attributed to nonspecific adsorption nor to its inclusion in protein aggregates. We conclude that both lectin-oligosaccharide and polypeptide-based interactions occur between calnexin and diverse proteins in vivo and that the strength of the latter interaction varies substantially between protein substrates.
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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".