Stereo view of the AAZ-binding site in HpαCA and comparison to other αCAs.

<p>A: The (mFo-DFc) sigmaA-weighted [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127149#pone.0127149.ref032" target="_blank">32</a>] electron density for AAZ bound to HpαCA is shown in green. The map was calculated at 2.0-Å resolution and contoured at 3.0-σ level. The AAZ molecule is shown in all-atom ball-and-stick representation with carbon atoms coloured orange. Amino acid residues that interact with AAZ are shown in stick representation. The catalytic zinc ion that is coordinated tetrahedrally (black dash lines) is shown as a black sphere. Hydrogen bonds are shown as blue dashed lines. B: Stereo view of the inhibitor-binding sites of the superimposed HpαCA/AAZ (black), SspCA/AAZ (red), TaCA/AAZ (blue) and HCAII/AAZ (green) complexes. The diagram illustrates the remarkably similar mode of AAZ binding, particularly around the sulfonamide moiety which coordinates the zinc ion. Residues are labeled in HpαCA. C: Stereo view of the superposition of the active site regions of HpαCA (red) and HCAII (blue for the free enzyme, green for the complex with CO₂). Residues and water molecules are labeled in HCAII. The “deep” water (Wat338), catalytic water (Wat263) and Wat318 observed in the active site of free HCAII are shown as blue spheres. The CO₂ (substrate) observed in the crystal structure of the HCAII/CO₂ complex is shown in green. The zinc ion (black sphere) is only shown in the free HCAII structure for clarity.