Molecular surface representations for the active site in the EcDHNA:NP and SaDHNA:NP complexes. (A) Active site structure in the EcDHNA:NP complex. (B) Active site structure in the SaDHNA:NP complex. The NP molecules and two variable amino acid side-chains are shown as stick models in atomic color scheme (carbon in green for EcDHNA and in cyan for SaDHNA, nitrogen in blue, and oxygen in red). The side-chains are also highlighted with transparent atomic surfaces. The illustration was made using PyMOL (Delano Scientific, San Carlos, CA, USA).