The topology of the C-terminal sections of the NCX1 Na<sup>+</sup>/Ca<sup>2+</sup>exchanger and the NCKX2 Na<sup>+</sup>/Ca<sup>2+</sup>-K<sup>+</sup>exchanger
Bibliographic record
Abstract
Mammalian Na (+) /Ca ( 2+) (NCX) and Na (+) /Ca ( 2+) -K (+) exchangers (NCKX) are polytopic membrane proteins that play critical roles in calcium homeostasis in many cells. Although hydropathy plots for NCX and NCKX are very similar, reported topological models for NCX1 and NCKX2 differ in the orientation of the three C-terminal transmembrane segments (TMS). NCX1 is thought to have 9 TMS and a re-entrant loop, whereas NCKX2 is thought to have 10 TMS. The current topological model of NCKX2 is very similar to the 10 membrane spanning helices seen in the recently reported crystal structure of NCX_MJ, a distantly related archaebacterial Na (+) /Ca ( 2+) exchanger. Here we reinvestigate the orientation of the three C-terminal TMS of NCX1 and NCKX2 using mass-tagging experiments of substituted cysteine residues. Our results suggest that NCX1, NCKX2 and NCX_MJ all share the same 10 TMS topology.
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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 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 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".