Structural asymmetry in the magnesium channel CorA points to sequential allosteric regulation
Bibliographic record
Abstract
Magnesium ions (Mg(2+)) are essential for life, but the mechanisms regulating their transport into and out of cells remain poorly understood. The CorA-Mrs2-Alr1 superfamily of Mg(2+) channels represents the most prevalent group of proteins enabling Mg(2+) ions to cross membranes. Thermotoga maritima CorA (TmCorA) is the only member of this protein family whose complete 3D fold is known. Here, we report the crystal structure of a mutant in the presence and absence of divalent ions and compare it with previous divalent ion-bound TmCorA structures. With Mg(2+) present, this structure shows binding of a hydrated Mg(2+) ion to the periplasmic Gly-Met-Asn (GMN) motif, revealing clues of ion selectivity in this unique channel family. In the absence of Mg(2+), TmCorA displays an unexpected asymmetric conformation caused by radial and lateral tilts of protomers that leads to bending of the central, pore-lining helix. Molecular dynamics simulations support these movements, including a bell-like deflection. Mass spectrometric analysis confirms that major proteolytic cleavage occurs within a region that is selectively exposed by such a bell-like bending motion. Our results point to a sequential allosteric model of regulation, where intracellular Mg(2+) binding locks TmCorA in a symmetric, transport-incompetent conformation and loss of intracellular Mg(2+) causes an asymmetric, potentially influx-competent conformation of the channel.
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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 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| 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".