Periplasmic Loops of Osmosensory Transporter ProP in <i>Escherichia coli</i> Are Sensitive to Osmolality
Bibliographic record
Abstract
ProP is an osmosensory transporter. The activities of ProP and ProP*, a cysteine-less, His(6)-tagged ProP variant, increase with osmotic pressure in cells and proteoliposomes. In proteoliposomes, ProP activity is osmolality-dependent only if the magnitude of the membrane potential (DeltaPsi) exceeds 100 mV. Some amino acid replacements rendered ProP activity osmolality-insensitive [e.g., Y44M in transmembrane segment 1 (TMI); S62C in periplasmic loop 1 (loop P1)], whereas others elevated the osmolality at which ProP activates (e.g., A59C). This suggested that the environments and/or conformations of TMI and loop P1 might be osmolality-dependent. This report correlates structural dynamics of ProP with osmoregulation of its transport activity. Residues in periplasmic loops were replaced with Cys, and changes in their environments were detected by monitoring their reactivities with N-ethylmaleimide (NEM). Increasing osmolality markedly increased the NEM reactivity of some Cys residues (e.g., C59, loop P1; C415-C418, loop P6) but not others (e.g., C293, loop P4; C348, loop P5). The NEM reactivity of C62 was insensitive to osmolality, as expected. Substitution Y44M rendered the transport activities of ProP*-A59C and ProP*-Q415C, and the NEM reactivities of the introduced Cys, osmolality-insensitive. Furthermore, osmolality did not affect the reactivity of C59 in cells lacking a protonmotive force, consistent with evidence that DeltaPsi is required for osmosensing by ProP. These results indicate that the osmotically induced increases in NEM reactivity of C59 and C415 in energized bacteria are due to a conformational change of ProP in response to osmolality. They therefore constitute the first direct evidence of an osmotically induced conformational change associated with osmosensing by a transporter.
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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 | 0.000 |
| 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 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".