Extended Data Fig. 6: Active site architecture of gamma-type carbonic anhydrases.
a, γCA-domain of complex I from Arabidopsis. The active site is located at the interface between the γCA2 (yellow) and γCA1 (orange) subunit. The three conserved histidines (H130 of γCA1, H107 and H135 of γCA2) coordinate a zinc ion (Zn) together with one water molecule (w) in a tetrahedral geometry (metal coordination shown by red dotted lines). The water molecule forms a hydrogen bond (black dotted lines) with an additional water that interacts with the polypeptide backbone of γCA2 V108 and residue γCA2 K110. A third water is coordinated by γCA2 D153. There appears to be no bound HCO3−. Coordination of Zn, the hydrogen network and conserved amino acids including Q101, N99, Y207 and S203 resemble the active Zn-CamH site of Pyrococcus horikoshii. b, Pyrococcus horikoshii Zn-CamH. Left: without HCO3− (PDB: 1V3W), right: with HCO3− (PDB: 1V67). c, Methanosarcina thermophila Zn-Cam. Left: without HCO3− (PDB: 1QRG), right: with HCO3− (PDB: 1QRL). Note that the zinc ion at the Cam site is coordinated by two further water molecules compared to the γCA2/γCA1 site in Arabidopsis and CamH. In addition, E62 and E84 that are known to be important for proton release replace V89 and K110 of γCA2 and I47 and H68 of CamH. d, Methanosarcina thermophila Co-Cam. Left: without HCO3− (PDB: 1QQ0), right: with HCO3− (PDB: 1QRE). A cobalt ion (Co) is coordinated by the three conserved histidines and three additional water molecules. In contrast to the heterotrimeric CA domain of Arabidopsis complex I, the bacterial Cam/CamH enzymes are homotrimers with three identical active sites located at the three subunit interfaces.
