Unprecedented carbonic anhydrase inhibition mechanism: Targeting histidine 64 side chain through a halogen bond
2025

New Mechanism for Inhibiting Carbonic Anhydrase with Bithionol

publication Evidence: moderate

Author Information

Author(s): Roberto Paciotti, Simone Carradori, Andreas Angeli, Ilaria D'Agostino, Marta Ferraroni, Cecilia Coletti, Claudiu T. Supuran

Primary Institution: Department of Pharmacy “G. d'Annunzio” University of Chieti‐Pescara

Hypothesis

Bithionol's halogen atoms and hydroxyl groups can interact with carbonic anhydrase enzymes to inhibit their activity.

Conclusion

Bithionol shows micromolar inhibition of human carbonic anhydrase II through a unique halogen-bonding interaction with the His64 residue.

Supporting Evidence

  • Bithionol showed a micromolar inhibition of specific human carbonic anhydrases.
  • X-ray crystallography revealed a halogen-bond interaction between bithionol and His64 in hCA II.
  • Quantum mechanics calculations estimated the strength of the halogen bond to be approximately 2.9 kcal/mol.
  • Bithionol was inactive against hCA III due to mutations that prevent halogen bonding.

Takeaway

Bithionol is a small molecule that can stop certain enzymes in our body from working by using a special bond with a part of the enzyme.

Methodology

Bithionol was tested on human carbonic anhydrases using stopped-flow techniques and X-ray crystallography to study its binding interactions.

Limitations

Bithionol is a weak inhibitor with low selectivity over other carbonic anhydrases.

Digital Object Identifier (DOI)

10.1002/ardp.202400776

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