Structural Analysis of Mg2+ and Ca2+ Binding to CaBP1, a Neuron-specific Regulator of Calcium Channels
Bibliographic record
Abstract
CaBP1 (calcium-binding protein 1) is a 19.4-kDa protein of the EF-hand superfamily that modulates the activity of Ca(2+) channels in the brain and retina. Here we present data from NMR, microcalorimetry, and other biophysical studies that characterize Ca(2+) binding, Mg(2+) binding, and structural properties of recombinant CaBP1 purified from Escherichia coli. Mg(2+) binds constitutively to CaBP1 at EF-1 with an apparent dissociation constant (K(d)) of 300 microm. Mg(2+) binding to CaBP1 is enthalpic (DeltaH = -3.725 kcal/mol) and promotes NMR spectral changes, indicative of a concerted Mg(2+)-induced conformational change. Ca(2+) binding to CaBP1 induces NMR spectral changes assigned to residues in EF-3 and EF-4, indicating localized Ca(2+)-induced conformational changes at these sites. Ca(2+) binds cooperatively to CaBP1 at EF-3 and EF-4 with an apparent K(d) of 2.5 microM and a Hill coefficient of 1.3. Ca(2+) binds to EF-1 with low affinity (K(d) >100 microM), and no Ca(2+) binding was detected at EF-2. In the absence of Mg(2+) and Ca(2+), CaBP1 forms a flexible molten globule-like structure. Mg(2+) and Ca(2+) induce distinct conformational changes resulting in protein dimerization and markedly increased folding stability. The unfolding temperatures are 53, 74, and 76 degrees C for apo-, Mg(2+)-bound, and Ca(2+)-bound CaBP1, respectively. Together, our results suggest that CaBP1 switches between structurally distinct Mg(2+)-bound and Ca(2+)-bound states in response to Ca(2+) signaling. Both conformational states may serve to modulate the activity of Ca(2+) channel targets.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 teacher head, 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".