Structural and Functional Analysis of Transmembrane Segment IV of the Salt Tolerance Protein Sod2*
Bibliographic record
Abstract
Sod2 is the plasma membrane Na + /H + exchanger of the fission yeast Schizosaccharomyces pombe . It provides salt tolerance by removing excess intracellular sodium (or lithium) in exchange for protons. We examined the role of amino acid residues of transmembrane segment IV (TM IV) ( 126 FPQINFLGSLLIAGCITSTDPVLSALI 152 ) in activity by using alanine scanning mutagenesis and examining salt tolerance in sod2 -deficient S. pombe . Two amino acids were critical for function. Mutations T144A and V147A resulted in defective proteins that did not confer salt tolerance when reintroduced into S. pombe . Sod2 protein with other alanine mutations in TM IV had little or no effect. T144D and T144K mutant proteins were inactive; however, a T144S protein was functional and provided lithium, but not sodium, tolerance and transport. Analysis of sensitivity to trypsin indicated that the mutations caused a conformational change in the Sod2 protein. We expressed and purified TM IV (amino acids 125–154). NMR analysis yielded a model with two helical regions (amino acids 128–142 and 147–154) separated by an unwound region (amino acids 143–146). Molecular modeling of the entire Sod2 protein suggested that TM IV has a structure similar to that deduced by NMR analysis and an overall structure similar to that of Escherichia coli NhaA. TM IV of Sod2 has similarities to TM V of the Zygosaccharomyces rouxii Na + /H + exchanger and TM VI of isoform 1 of mammalian Na + /H + exchanger. TM IV of Sod2 is critical to transport and may be involved in cation binding or conformational changes of the protein. Background: Sod2 is the salt tolerance protein of Schizosaccharomyces pombe . Results: Alanine scanning mutagenesis and structural analysis demonstrated that amino acids 144–147 are in an extended region of transmembrane segment IV and are critical for function. Conclusion: Mutations in transmembrane segment IV affect Sod2 cation transport. Significance: TM IV of Sod2 has conserved structures with other Na + /H + exchangers important in salt tolerance.
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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) | 0.001 | 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".