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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.

IUCrJ
Volume 7| Part 2| March 2020| Pages 287-293
ISSN: 2052-2525
https://doi.org/10.1107/S2052252520000986