Sordaria macrospora carbonic anhydrases.

Sordaria macrospora, a coprophylous fungus used for the last three decades as a model organism for studying fruiting body development of fungi, encodes for four carbonic anhydrases (CAs, EC 4.2.1.1), CAS1-CAS4. CAS1-CAS3 are β-CAs and were investigated in detail in the last years, whereas CAS4, an α-class enzyme, was less investigated. All of them are crucial for the fungus, as the mutant lacking the genes encoding for these four enzymes showed a drastically reduced vegetative growth rate compared to the wild type organism. CAS4 is a secreted protein, CAS2 is mitochondrial, whereas CAS1 and CAS3 are cytosolic enzymes. The catalytic activity of CAS1-CAS3 for the CO₂ hydration reaction showed that all of them possess a significant activity, with CAS3 being the most effective catalyst. The X-ray crystal structures of CAS1 and CAS2 were also obtained, showing that the two enzymes are tetramers (dimers of dimers) with an open active site in the case of CAS1 and a closed one for CAS2, similar to other plant/fungal/bacterial β-CAs studied so far. Detailed anion and sulfonamide inhibition studies were reported for all three β-Cas, which led to the identification of several effective inhibitors. Potential biotechnological applications of these enzymes for carbon (CO₂) capture are also discussed.

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