A thylakoid‐located carbonic anhydrase regulates <scp>CO</scp><sub>2</sub> uptake in the cyanobacterium <i>Synechocystis</i> sp. PCC 6803
Bibliographic record
Abstract
Summary Carbonic anhydrases (CAs) are involved in CO2 uptake and conversion, a fundamental process in photosynthetic organisms. Nevertheless, the mechanism underlying the regulation of CO2 uptake and intracellular conversion in cyanobacteria is largely unknown. We report the characterization of a previously unrecognized thylakoid‐located CA Slr0051 (EcaB) from the cyanobacterium Synechocystis sp. PCC 6803, which possesses CA activity to regulate CO2 uptake. Inactivation of ecaB stimulated CO2 hydration in the thylakoids, suppressed by the classical CA inhibitor acetazolamide. Absence of ecaB increased the reduced state of the photosynthetic electron transport system, lowered the rate of photosynthetic O2 evolution at high light (HL) and pH, and decreased the cellular affinity for extracellular inorganic carbon. Furthermore, EcaB was upregulated in cells grown at limiting CO2 concentration or HL in tandem with CupA. EcaB is mainly located in the thylakoid membranes where it interacts with CupA and CupB involved in CO2 uptake by converting it to bicarbonate. We propose that modulation of the EcaB level and activity in response to CO2 changes, illumination or pH reversibly regulates its conversion to HCO3 by the two CO2‐uptake systems (CupA, CupB), dissipating the excess HCO3− and alleviating photoinhibition, and thereby optimizes photosynthesis, especially under HL and alkaline conditions.
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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".