Identification of a Disulfide Bridge Linking the Fourth and the Seventh Extracellular Loops of the Na+/Glucose Cotransporter
Bibliographic record
Abstract
The Na+/glucose cotransporter (SGLT1) is an archetype for the SLC5 family, which is comprised of Na+-coupled transporters for sugars, myo-inositol, choline, and organic anions. Application of the reducing agent dithriothreitol (DTT, 10 mM) to oocytes expressing human SGLT1 affects the protein's presteady-state currents. Integration of these currents at different membrane potentials (Vm) produces a Q-V curve, whose form was shifted by +25 mV due to DTT. The role of the 15 endogenous cysteine residues was investigated by expressing SGLT1 constructs, each bearing a single mutation for an individual cysteine, in Xenopus oocytes, using two-microelectrode voltage-clamp electrophysiology and fluorescent labeling. 12 of the 15 mutants were functional and could be separated into three distinct groups based on the effect of the mutation on the Q-V curve: four mutants did not perturb the transferred charge, six mutants shifted the Q-V curve towards negative potentials, and two mutants (C255A and C511A) produced a shift in the positive direction that was identical to the shift produced by DTT on the wild-type (wt) SGLT1. The double mutant C(255,511)A confirms that the effects of each single mutant on the Q-V curve were not additive. With respect to wt SGLT1, the apparent affinities for alpha-methylglucose (alphaMG) were increased in a similar manner for the single mutants C255A and C511A, the double mutant C(255,511)A as well as for wt SGLT1 treated with DTT. When exposed to a maleimide-based fluorescent probe, wt SGLT1 was not significantly labeled but mutants C255A and C511A could be clearly labeled, indicating an accessible cysteine residue. These residues are presumed to be C511 and C255, respectively, as the double mutant C(255,511)A could not be labeled. These results strongly support the hypothesis that C255 and C511 form a disulfide bridge in human SGLT1 and that this disulfide bridge is involved in the conformational change of the free carrier.
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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 | 0.000 |
| 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".