Calcium Binding to Skeletal Muscle Troponin C and the Regulation of Muscle Contraction
Bibliographic record
Abstract
Skeletal muscle contraction is initiated by Ca2+ ion binding to troponin C (TnC), a protein of the thin filament. Our three-dimensional structure determination of turkey skeletal TnC at 2.8 A resolution revealed an extended molecule consisting of two domains connected through a long nine-turn alpha-helix. The C-terminal domain has two Ca2+ ions bound in the expected manner of EF hands, whereas the N-terminal regulatory domain is Ca2+-free with a helix-loop-helix conformation different from that of an EF hand. The refinement of TnC at 2.2 A resolution highlights the intricate hydrogen-bonded network common to the Ca2+-bound loops and provides an explanation for the presence of a water molecule in the 5th coordination position of the Ca2+ ion. We propose that Ca2+ binding to the regulatory domain is accompanied by a conformational transition by which its structure becomes similar to that of the C-terminal domain. Dramatic movements of residues in the B and C helices and the connecting peptide of up to 14 A constitute the bulk of this change. A hydrophobic site that could be the site of interaction with troponin I is thereby exposed. We have also demonstrated that this model of the Ca2+-bound conformation can be reached from the Ca2+-free state without having to surmount large energy barriers.
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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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 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".