A single residue exerts two contrasting effects on autoinhibition of HCN channels
Bibliographic record
Abstract
Hyperpolarization‐activated cation (HCN) channels regulate electrical activity in the brain and heart in a cAMP‐dependent manner. The voltage‐gating of these channels is mediated by a transmembrane (TM) region but is additionally regulated by direct binding of cAMP to a cyclic nucleotide‐binding (CNB) fold in the cytoplasmic C‐terminal region. In the unliganded form, the CNB fold mediates an autoinhibitory mechanism that kinetically and thermodynamically stabilizes the closed state, and cAMP binding relieves this inhibition. This autoinhibition is an important regulatory mechanism, relief of which provides a molecular mechanism for how cAMP potentiation occurs. The magnitude of this autoinhibition can be calculated by comparing thermodynamic or kinetic parameters of a channel to the parameters from a channel that is autoinhibition‐free due to truncation of the CNB fold. Recently, I have found that the magnitude of autoinhibition is regulated by interdomain interactions between the C‐terminal region and TM region structures. Specifically, the magnitude of both kinetic and thermodynamic autoinhibition was augmented by replacing the TM region of the HCN2 channel with the TM region of HCN4. I hypothesized that interdomain interactions between the HCN4 TM region and charged residues in the C‐linker, which connects the CNB fold to the TM region, can modify the magnitude of autoinhibition. I used site directed mutagenesis to identify that the E457 residue formed an electrostatic interaction with the HCN4 TM region to stabilize the open state. This residue also has an important role in both the kinetic and thermodynamic components of the autoinhibition mechanism. A charge reversal mutation (E457R) limited the thermodynamic effect of autoinhibition while augmenting the kinetic effect of autoinhibition. Overall, this work suggests that the molecular mechanisms of autoinhibition must include participation of TM region structures and provides functional evidence for interdomain interactions that facilitate HCN channel regulation by CNB fold‐mediated mechanisms. Support or Funding Information NSERC, Simon Fraser University
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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 | 0.001 |
| 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; 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".