Crystal structure of α-carbonic anhydrase from<i>Chlamydomonas reinhardtii</i>
Bibliographic record
Abstract
Carbonic anhydrase (CA) plays important roles in biological processes such as photosynthesis, respiration, secretion of HCO3 -, pH homeostasis and ion exchange.The proteins commonly contain a zinc ion in the active site for catalyzing the hydration of CO2 and vice versa.It is known that there are three classes of CA, designated α-, βand γ-CAs, depending on the amino acid sequence similarities.The α-class is different from others in the structural architecture.Furthermore, even in the α-class, the enzyme from unicellular green alga, Chlamydomonas reinhardtii (chCA) is unique in posttranslational modifications that it is glycosylated and spliced into two peptides.Such glycosylations are found in only mammalian CAs but they are not spliced.To reveal the structural details and the role of N-glycosylation, an X-ray analysis of chCA has been performed.chCA is a homodimeric protein, the two subunits being crystallographically independent.In each subunit, residues from Ser298 to Asn345 are spliced to separate into long and short peptides.The two subunits are, however, linked together by a disulfide bond.In the catalytic site, a zinc ion is bound to the three conserved His163, His165 and His182 in a tetrahedral configuration.A water molecule is trapped at the fourth position of the Zn atom.The electron density maps indicate that N-glycosylations occur at the three sites, Asn101, Asn135 and Asn297.This structure is the first example of CA attached to N-glycosides.chCA molecules are interacted to each other with a six-fold screw symmetry to form a long column.Furthermore, they are fused through the lateral interactions like a beehive.Each catalytic site is exposed to the central tunnel.It suggests that chCA in the crystalline state also catalyze the reaction.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".