Role of Cysteine Residues in the NCKX2 Na<sup>+</sup>/Ca<sup>2+</sup>−K<sup>+</sup>Exchanger: Generation of a Functional Cysteine-Free Exchanger
Bibliographic record
Abstract
Cysteine residues play an important role in many proteins, either in enzymatic activity or by mediating inter- or intramolecular interactions. The Na(+)/Ca(2+)-K(+) exchanger plays a critical role in Ca(2+) homeostasis in retinal rod (NCKX1) and cone (NCKX2) photoreceptors by extruding Ca(2+) that enters rod and cone cells via the cGMP-gated channels. NCKX1 and NCKX2 contain five highly conserved cysteine residues. The objectives of this study were threefold: (1) to examine the importance of cysteine residues in NCKX2 protein function; (2) to examine their role in the interaction between NCKX2 and the CNGA subunit of the cGMP-gated channel; and (3) to generate a functional cysteine-free NCKX2 protein. The latter will facilitate structural studies taking advantage of the unique chemistry of the thiol group following insertion of cysteine residues at specific positions in the cysteine-free background. We generated a cysteine-free NCKX2 mutant protein that showed normal protein synthesis and processing and approximately 50% wild-type cation transport function. Cysteine residues were also not critical for the formation of NCKX2 homo-oligmers or NCKX2 hetero-oligomers with the CNGA subunit of the cGMP-gated channel. Our results appear to rule out a critical importance of an intramolecular disulfide linkage in NCKX2 protein synthesis and folding as had been reported before.
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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 | 0.000 |
| 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 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".