Two dimensional crystallization of calcium transport regulatory complexes
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Bibliographic record
Abstract
Phospholamban and sarcolipin physically interact with the sarcoplasmic reticulum calcium pump (SERCA) and differentially regulate contractility in smooth, skeletal, and cardiac muscle. While mutagenesis and cross-linking studies have provided insight into the mechanism of interaction, we lack a molecular understanding of these regulatory complexes. We have compared two crystal forms of SERCA in the absence and presence of phospholamban by electron cryo-microscopy. Our previous studies with phospholamban utilized both small helical crystals [1] and large two-dimensional crystals [2], where the fundamental units of both crystal forms were found to be anti-parallel dimer ribbons of SERCA molecules. The SERCA dimer ribbons have been known for decades as a rigid assembly of calcium-free SERCA molecules induced by the addition of decavanadate. While the lattice formed by the SERCA dimer ribbons is different in the helical (p2) and two-dimensional crystals (p22121), we now show that a phospholamban oligomer interacts with SERCA in a similar manner in both crystal types. With this information, we next undertook a structural investigation of SERCA and sarcolipin in the large two-dimensional crystals. Both wild-type and a gain-of-function mutant (Asn4-to-Ala) mutant of sarcolipin were utilized. Projection maps were determined for SERCA in the presence of sarcolipin to a resolution of 8.5 Å and were most consistent with a pentameric state for sarcolipin. While both phospholamban and sarcolipin interacted with transmembrane segment M3 of SERCA, the interaction of the sarcolipin pentamer was mediated by an additional density consistent with a sarcolipin monomer.
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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 it