FIGURE 4.

SMMA active site. a, catalytic (red) and related subsite residues (cyan) are shown as sticks. The hydrogen bond network in the active site is shown with the additional aromatic N′ domain residues (blue). b, a surface representation of the active site pocket is shown with a hypothetical CD molecule modeled at the active site. c, a structural comparison of the active sites in SMMA (left) and NPase (right) from B. stearothermophilus (Protein Data Bank entry 1J0H); the substrate-binding grooves at the active sites are shown.