Disrupting the network of co-evolving amino terminal domain residues relieves mitochondrial calcium uptake inhibition by MCUb
Bibliographic record
Abstract
The regulatory mechanisms of the mitochondrial calcium uniporter complex (mtCU), the predominant channel mediating calcium (Ca 2 + ) flux into the matrix, are critical for bioenergetics and cell fate. The pore-forming components of mtCU are the mitochondrial Ca 2+ uniporter (MCU) subunit and the MCU dominant-negative beta (MCUb) subunit. Despite both MCU paralogs having conserved Asp-Ile-Met-Glu motifs responsible for Ca 2+ selectivity, MCUb mediates only low Ca 2+ conduction and has been characterized as an inhibitory subunit. We previously identified the MCU amino-terminal domain (NTD) as a negative feedback regulator of mtCU upon divalent cation binding but the role of the MCUb-NTD remains unknown. Thus, to gain mechanistic insight into the competing MCU and MCUb functions, we here studied the divalent cation binding properties of the MCU- and MCUb-NTDs that tightly interact within and between tetrameric channels. First, we resolved a high-resolution MCU-NTD crystal structure in the absence of divalent ions at 1.6 Å, using this structure to model the homologous MCUb-NTD. Further, we conducted 1 μs all-atom molecular dynamics (MD) simulations in the presence and absence of Ca 2+ and Mg 2+ ions, not only finding increased MCU-NTD stability at high temperatures compared to MCUb-NTD but also discrete Ca 2+ -binding sites on the two domains. Remarkably, the distinct Ca 2+ binding site on the central α-helix of MCUb-NTD was also identified in a functional sector of co-evolving residues, with either direct mutation to the coordinating residues or mutation to a separate site within the sector disrupting Ca 2+ binding in silico and in vitro as well as enhancing mitochondrial Ca 2+ uptake in cellulo . Thus, we reveal that matrix Ca 2+ binding to both the MCU-NTD and MCUb-NTD promote mtCU inhibition through disparate interaction sites, highlighting the evolution of discrete feedback regulation mechanisms to precisely control mtCU function.
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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 | 0.001 |
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".