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Figure 1
Structure of Zn– and Cu–CAII: active site and water network. (a) Zn–CAII. The zinc metal is stabilized by three histidines (His94, His96 and His119). His64 is depicted in its dual `in' and `out' conformations. The N terminus (residues 1–4) is disordered. The substrate CO2 is shown bound adjacent to the zinc, stabilized by the hydro­phobic pocket (Domsic et al., 2008BB11). (b) Cu–CAII. The copper metal (T-2 site) is stabilized by the same three histidines as the zinc. Also, His64 was observed in dual conformations. The NO2− bound with an oxygen and a nitro­gen interacting with the copper. The water network resembles that observed in Zn–CAII, with the exception of the extended water network (W4 and W5), creating a hydrogen-bonding network spanning from the N terminus to the active site. The N terminus is ordered, forming a pseudo-porphyrin ring around a second copper (T-2 site). The catalytic metals are depicted as spheres: zinc (magenta) and copper (brown). The hydro­phobic residues (Ile91, Val121, Phe131, Val135, Leu141, Val143, Leu198, Pro202, Leu204, Val207 and Trp209) are highlighted as orange and the hydro­philic residues (Asn62, His64, Asn67, Gln92, Thr199 and Thr200) as violet. The active-site solvent network (W1, W2, W3a and W3b) is depicted as red spheres and the extended water network (W4 and W5) is shown in the Cu–CAII substituted structure.

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