Mutational Analysis of Ionizable Residues Proximal to the Cytoplasmic Interface of Membrane Spanning Domain 3 of the Multidrug Resistance Protein, MRP1 (ABCC1)
Bibliographic record
Abstract
The multidrug resistance protein MRP1 is an ATP-dependent transporter of organic anions and chemotherapeutic agents. A significant number of ionizable amino acids are found in or proximal to the 17 transmembrane (TM) helices of MRP1, and we have investigated 6 of these at the cytoplasmic interface of TM13-17 for their role in MRP1 expression and transport activity. Opposite charge substitutions of TM13 Arg(1046) and TM15 Arg(1131) did not alter MRP1 expression nor did they substantially affect activity. In contrast, opposite charge substitutions of TM16 Arg(1202) and Glu(1204) reduced protein expression by >80%; however, MRP1 expression was not affected when Arg(1202) and Glu(1204) were replaced with neutral or same-charge residues. In addition, organic anion transport levels of the R1202L, R1202G, and R1202K mutants were comparable with wild-type MRP1. In contrast, organic anion transport by E1204L was substantially reduced, whereas transport by E1204D was comparable with wild-type MRP1, with the notable exception of GSH. Opposite charge substitutions of TM16 Arg(1197) and TM17 Arg(1249) did not affect MRP1 expression but substantially reduced transport. Mutants containing like-charge substitutions of Arg(1197) or Arg(1249) were also transport-inactive and no longer bound leukotriene C(4). In contrast, substrate binding by the transport-compromised E1204L mutant remained intact. Furthermore, vanadate-induced trapping of azido-ADP by E1204L was dramatically increased, indicating that this mutation may cause a partial uncoupling of the catalytic and transport activities of MRP1. Thus, Glu(1204) serves a dual role in membrane expression of MRP1 and a step in its catalytic cycle subsequent to initial substrate binding.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| 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 | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".