Deuterium NMR Reveals Helix Packing Interactions in Phospholamban
Bibliographic record
Abstract
Phospholamban is an integral membrane protein having a single membrane-spanning helix which forms a pentameric complex in cardiac and smooth muscle cell membranes. Deuterium NMR measurements of leucine residues in the transmembrane domain of the protein provide a novel approach for establishing the rotational orientation of the phospholamban monomer within the complex. At 5 °C, the spectra of Leu43 and Leu44 are similar and exhibit a quadrupole splitting of 33 kHz. This splitting is slightly narrower than the ∼40 kHz splitting which results solely from rapid methyl group rotation. The deuterium line shape of Leu42 has lost the distinctive 33-kHz quadrupole splitting due to increased librational motion of the side chain and/or rotation about the C α −C β and C β −C γ bonds. The observed line shapes of the three consecutive leucine residues in phospholamban are consistent with Leu42 being oriented toward the lipids, where it exhibits fewer steric contacts, and Leu43 and Leu44 being oriented toward helix interfaces which restrict their motion. Possible packing arrangements of the three transmembrane leucine residues in the phospholamban pentamer are examined using computational methods to assess the packing restrictions of the leucine side chains. The results are discussed in terms of models of the phospholamban pentamer previously proposed on the basis of mutational data.
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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".