Fig 7.

Crystal structure and models of CS₂ hydrolases. (A) Resolved crystal structure of the CS₂ hydrolase from Acidianus strain A1-3 and structural models of the CS₂ hydrolases from A. thiooxidans strain G8 (B) and strain S1p (C), modeled using the hexadecameric structure of the Acidianus A1-3 CS₂ hydrolase as a template. The two octameric interlocking rings forming the hexadecamer are shown in different colors. (D, E, F) Details of octamers showing the narrow hydrophobic entrance tunnels (pink) to the Zn-containing active site in the Acidianus CS₂ hydrolase (D) and in the models of the G8 (E) and S1p (F) CS₂ hydrolases. The Zn atoms are indicated by pink spheres. (G, H, I) Views of the tunnels looking in from the entrances to the active sites, showing the three monomers (two shades of gray and blue) and the residues (red) forming the tunnel in the Acidianus CS₂ hydrolase (G) and in the models of the G8 hydrolases (blue, cyan, and green monomers) (H) and the S1p CS₂ hydrolases (yellow, orange, and red monomers) (I).