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Figure 2
Active site of Zn– and Cu–CAII (T-2 site) with bound substrate, CO2 and NO2, respectively. (a) CO2 binding site in Zn–CAII active site (adapted from PDB entries 3ks3, Avvaru et al., 2010BB7; 5yui, Kim et al., 2016BB23). CO2 binds adjacent to the zinc, ∼2.8 Å from the catalytic zinc-bound solvent. The CO2 is stabilized via interactions with residues Val121, Val143, Leu198 and Trp209. Thr199 also forms a hydrogen bond with CO2 via its nitro­gen. (b) NO2 binding site in Cu–CAII active site. NO2 binds directly to the copper, displacing the copper-bound solvent. It binds in a `side-on' conformation via an oxygen and a nitro­gen, 2.1 and 2.8 Å from the copper, respectively. However, solvent W1 retains its position and forms hydrogen bonds with an oxygen of NO2. Thr199 forms two hydrogen bonds with the bound NO2 while Leu198 also forms stabilizing interactions. The catalytic metals are depicted as spheres: zinc (magenta) and copper (brown). The active-site solvent molecules are depicted as red spheres.

Volume 7| Part 2| March 2020| Pages 287-293
ISSN: 2052-2525