Changes in Accessibility of Cytoplasmic Substances to the Pore Associated with Activation of the Cystic Fibrosis Transmembrane Conductance Regulator Chloride Channel
Bibliographic record
Abstract
Opening of the cystic fibrosis transmembrane conductance regulator Cl(-) channel is dependent both on phosphorylation and on ATP binding and hydrolysis. However, the mechanisms by which these cytoplasmic regulatory factors open the Cl(-) channel pore are not known. We have used patch clamp recording to investigate the accessibility of cytoplasmically applied cysteine-reactive reagents to cysteines introduced along the length of the pore-lining sixth transmembrane region (TM6) of a cysteine-less variant of cystic fibrosis transmembrane conductance regulator. We find that methanethiosulfonate (MTS) reagents modify irreversibly cysteines substituted for TM6 residues Phe-337, Thr-338, Ser-341, Ile-344, Val-345, Met-348, Ala-349, Arg-352, and Gln-353 when applied to the cytoplasmic side of open channels. However, the apparent rate of modification by internal [2-sulfonatoethyl] methanethiosulfonate (MTSES), a negatively charged MTS reagent, is dependent on the activation state of the channels. In particular, cysteines introduced far along the axis of TM6 from the inside (T338C, S341C, I344C) showed no evidence of significant modification even after prolonged pretreatment of non-activated channels with internal MTSES. In contrast, cysteines introduced closer to the inside of TM6 (V345C, M348C) were readily modified in both activated and non-activated channels. Access of a permeant anion, Au(CN)(2)(-), to T338C was similarly dependent upon channel activation state. The pattern of MTS modification we observe allows us to designate different pore-lining amino acid side chains to distinct functional regions of the channel pore. One logical interpretation of these findings is that cytoplasmic access to residues at the narrowest region of the pore changes concomitant with activation.
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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 | 0.001 | 0.003 |
| 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 | 0.001 |
| 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 teacher head, 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".