The Solution Structure of a Plant Calmodulin and the CaM-binding Domain of the Vacuolar Calcium-ATPase BCA1 Reveals a New Binding and Activation Mechanism
Bibliographic record
Abstract
The type IIb class of plant Ca(2+)-ATPases contains a unique N-terminal extension that encompasses a calmodulin (CaM) binding domain and an auto-inhibitory domain. Binding of Ca(2+)-CaM to this region can release auto-inhibition and activates the calcium pump. Using multidimensional NMR spectroscopy, we have determined the solution structure of the complex of a plant CaM isoform with the CaM-binding domain of the well characterized Ca(2+)-ATPase BCA1 from cauliflower. The complex has a rather elongated structure in which the two lobes of CaM do not contact each other. The anchor residues Trp-23 and Ile-40 form a 1-8-18 interaction motif. Binding of Ca(2+)-CaM gives rise to the induction of two helical parts in this unique target peptide. The two helical portions are connected by a highly positively charged bend region, which represents a relatively fixed angle and positions the two lobes of CaM in an orientation that has not been seen before in any complex structure of calmodulin. The behavior of the complex was further characterized by heteronuclear NMR dynamics measurements of the isotope-labeled protein and peptide. These data suggest a unique calcium-driven activation mechanism for BCA1 and other plant Ca(2+)-ATPases that may also explain the action of calcium-CaM on some other target enzymes. Moreover, CaM activation of plant Ca(2+)-ATPases seems to occur in an organelle-specific manner.
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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 | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| 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".