Transmembrane segment 1 of human P-glycoprotein contributes to the drug-binding pocket
Bibliographic record
Abstract
P-glycoprotein (P-gp; ABCB1) actively transports a broad range of structurally unrelated compounds out of the cell. An important step in the transport cycle is coupling of drug binding with ATP hydrolysis. Drug substrates such as verapamil bind in a common drug-binding pocket at the interface between the TM (transmembrane) domains of P-gp and stimulate ATPase activity. In the present study, we used cysteine-scanning mutagenesis and reaction with an MTS (methanethiosulphonate) thiol-reactive analogue of verapamil (MTS-verapamil) to test whether the first TM segment [TM1 (TM segment 1)] forms part of the drug-binding pocket. One mutant, L65C, showed elevated ATPase activity (10.7-fold higher than an untreated control) after removal of unchanged MTS-verapamil. The elevated ATPase activity was due to covalent attachment of MTS-verapamil to Cys65 because treatment with dithiothreitol returned the ATPase activity to basal levels. Verapamil covalently attached to Cys65 appears to occupy the drug-binding pocket because verapamil protected mutant L65C from modification by MTS-verapamil. The ATPase activity of the MTS-verapamil-modified mutant L65C could not be further stimulated with verapamil, calcein acetoxymethyl ester or demecolcine. The ATPase activity could be inhibited by cyclosporin A but not by trans-(E)-flupentixol. These results suggest that TM1 contributes to the drug-binding pocket.
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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 | 0.000 | 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 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".