Site-Directed Disulfide Mapping of Residues Contributing to the Ca<sup>2+</sup> and K<sup>+</sup> Binding Pocket of the NCKX2 Na<sup>+</sup>/Ca<sup>2+</sup>-K<sup>+</sup> Exchanger
Bibliographic record
Abstract
The Na+/Ca2+-K+ exchanger (NCKX) gene products are polytopic membrane proteins that utilize the existing cellular Na+ and K+ gradients to extrude cytoplasmic Ca2+. NCKX proteins are made up of two clusters of hydrophobic segments, both thought to consist of five putative membrane-spanning alpha-helices, and separated by a large cytoplasmic loop. The two most conserved regions within the NCKX sequence are known as the alpha1 and alpha2 repeats, and are found within the first and second set of transmembrane domains, respectively. The alpha repeats have previously been shown to contain residues critical for transport function. Here we used site-directed disulfide mapping to report that the alpha repeats are found in close proximity in three-dimensional space, bringing together key functional NCKX residues, e.g., the two critical acidic residues, Glu188 and Asp548. Glu188Cys in the alpha1 repeat could form a disulfide cross-link with Asp548Cys in the alpha2 repeat. Surprisingly, cysteine substitutions of Ser185 in the alpha1 repeat could form disulfide cross-links with cysteine substitutions of three residues in the alpha2 repeat (Ser545, Asp548, and Ser552), thought to cover close to two full turns of an alpha helix, implying an area of increased flexibility. Using the same method, Asp575, a residue critical for the K+ dependence of NCKX, was shown to be in the proximity of Ser185 and Glu188, consistent with its role in enabling K+ to bind to a single Ca2+ and K+ binding pocket.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.002 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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; both teacher heads agree on what is shown here.
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".