The Conformation of Calreticulin Is Influenced by the Endoplasmic Reticulum Luminal Environment
Bibliographic record
Abstract
In order to understand the dynamics of the endoplasmic reticulum (ER) luminal environment, we investigated the role of Ca 2+ , Zn 2+ , and ATP on conformational changes of calreticulin. Purified calreticulin was digested with trypsin in the presence or absence of Ca 2+ , Zn 2+ , and ATP. At low Ca 2+ concentration (<100 μm), calreticulin is rapidly and fully degraded by trypsin, indicating that under these conditions the protein is in a highly trypsin-susceptible conformation. Increasing Ca 2+ concentration up to 500 μm or 1 mm resulted in protection of the full-length calreticulin and in generation of the 27-kDa fragment highly resistant to trypsin digestion. The 27-kDa protease-resistant core of the protein represented the NH 2 -terminal half of calreticulin and was identified by its reactivity with specific antibodies and by NH 2 -terminal amino acid sequence analysis. Ca 2+ -dependent changes in calreticulin's sensitivity to proteolysis indicate that agonist-induced fluctuation in the free ER luminal Ca 2+ concentration may affect the protein conformation and function. Trypsin digestion of calreticulin in the presence of Zn 2+ resulted in the formation of a 17-kDa central protease-resistant core in the protein corresponding to the central region of the protein, indicating that under these conditions the N- and C-domains of the protein are in an extended conformation. Here we also show that calreticulin is an ATP-binding protein but that it does not contain detectable ATPase activity. Digestion of the protein with trypsin in the presence of Mg 2+ -ATP protects the full-length protein. These results indicate that calreticulin may undergo frequent, ion-induced conformation changes, which may affect its function and its ability to interact with other proteins in the lumen of the ER.
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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".