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Cadmium Carbonic Anhydrase (CdCA) Sustaining Life Using a Toxic Metal Ion www.ionicviper.org.

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Presentation on theme: "Cadmium Carbonic Anhydrase (CdCA) Sustaining Life Using a Toxic Metal Ion www.ionicviper.org."— Presentation transcript:

1 Cadmium Carbonic Anhydrase (CdCA) Sustaining Life Using a Toxic Metal Ion

2 Cadmium in Biological Systems Group 12 metal ions are considered essential (Zn 2+ ) or toxic (Cd 2+ and Hg 2+ ) to biological systems Typically, Cd 2+ ion presence in biological systems triggers glutathione (pictured below) and metallothionein sequestration

3 Carbonic Anhydrases Catalytic metalloproteins that interconvert CO 2 and H 2 O to HCO 3 - and H + Used in animals to transport CO 2 out of muscles and maintain blood pH balance Used by plants to concentrate CO 2 prior to photosynthesis Typically the active site comprises a tetrahedrally coordinated Zn 2+ ion surrounded by three histidine residues and one aqua or bicarbonato ligand Figure generated from PDB file 1CAM using Ligand Explorer

4 CdCAs in Marine Phytoplankton Oceanic environment of diatoms is Zn 2+ deficient Some diatom CAs have adapted to incorporate Cd 2+ in place of Zn 2+ based on bioavailability In accordance with HSAB theory, to accommodate the comparatively soft acid Cd 2+, the CA “ligand” now incorporates cysteine in place of two of the histidine residues Figure generated from PDB file 3BOB using Ligand Explorer

5 Summary HASB theory is exemplified by CA “ligands” that adapt to accommodate alternate active site metal ions (Zn 2+ vs. Cd 2+ ) Tetrahedrally coordinated active sites persist for CAs: Zn 2+ = 3 histidine residues and aqua or bicarbonato ligands Cd 2+ = 1 histidine and 2 cysteine residues, and aqua or bicarbonato ligands The resulting CAs are sufficiently robust to prevent metal ion release and subsequent toxicity


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