Molecular mechanisms of cutis laxa– and distal renal tubular acidosis–causing mutations in V-ATPase a subunits, ATP6V0A2 and ATP6V0A4
Bibliographic record
Abstract
The a subunit is the largest of 15 different subunits that make up the vacuolar H + -ATPase (V-ATPase) complex, where it functions in proton translocation. In mammals, this subunit has four paralogous isoforms, a 1– a 4, which may encode signals for targeting assembled V-ATPases to specific intracellular locations. Despite the functional importance of the a subunit, its structure remains controversial. By studying molecular mechanisms of human disease–causing missense mutations within a subunit isoforms, we may identify domains critical for V-ATPase targeting, activity and/or regulation. cDNA-encoded FLAG-tagged human wildtype ATP6V0A2 ( a 2) and ATP6V0A4 ( a 4) subunits and their mutants, a 2 P405L (causing cutis laxa), and a 4 R449H and a 4 G820R (causing renal tubular acidosis, dRTA), were transiently expressed in HEK 293 cells. N -Glycosylation was assessed using endoglycosidases, revealing that a 2 P405L , a 4 R449H , and a 4 G820R were fully N -glycosylated. Cycloheximide (CHX) chase assays revealed that a 2 P405L and a 4 R449H were unstable relative to wildtype. a 4 R449H was degraded predominantly in the proteasomal pathway, whereas a 2 P405L was degraded in both proteasomal and lysosomal pathways. Immunofluorescence studies disclosed retention in the endoplasmic reticulum and defective cell-surface expression of a 4 R449H and defective Golgi trafficking of a 2 P405L . Co-immunoprecipitation studies revealed an increase in association of a 4 R449H with the V 0 assembly factor VMA21, and a reduced association with the V 1 sector subunit, ATP6V1B1 (B1). For a 4 G820R , where stability, degradation, and trafficking were relatively unaffected, 3D molecular modeling suggested that the mutation causes dRTA by blocking the proton pathway. This study provides critical information that may assist rational drug design to manage dRTA and cutis laxa.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".