Amino Acid Residues Outside of the Pore Region Contribute to N-type Calcium Channel Permeation
Bibliographic record
Abstract
It is widely believed that the selectivity of voltage-dependent calcium channels is mainly controlled by amino acid residues contained within four p-loop motifs forming the pore of the channel. An examination of the amino acid sequences of high voltage-activated calcium channels reveals that their domain III S5-H5 regions contain a highly conserved motif with homology to known EF hand calcium binding proteins, hinting that this region may contribute to channel permeation. To test this hypothesis, we used site-directed mutagenesis to replace three conserved negatively charged residues in the N-type calcium channel alpha1B subunit (Glu-1321, Asp-1323, and Glu-1332) with positively charged amino acids (lysine and arginine) and studied their effect on ion selectivity using whole cell and single channel patch clamp recordings. Whereas the wild type channels conducted barium much more effectively than calcium, the mutant displayed nearly equal permeabilities for these two ions. Individual replacement of residue 1332 or a double substitution of residues 1321 and 1323 with lysine and arginine, respectively, were equally effective. Disruption of the putative EF hand motif through replacement of the central glycine residue (1326) with proline resulted in a similar effect, indicating that the responses observed with the triple mutant were not due to changes in the net charge of the channel. Overall, our data indicate that residues outside of the narrow region of the pore have the propensity to contribute to calcium channel permeation. They also raise the possibility that interactions of calcium ions with a putative calcium binding domain at the extracellular side of the channel may underlie the differential permeabilities of the channel for barium and calcium ions.
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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) | 0.001 | 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".