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Figure 5
Ligand binding of T2Cu sites. (a) A comparison of the T2Cu ligand binding of NO by SRX (Horrell et al., 2016BB23), of O2 by SRX (Fukuda et al., 2015BB14) and of O2 by SF-ROX. The AxNiR SF-ROX O2/superoxide is represented in blue, the AcNiR SRX NO in teal and the GtNiR SRX O2 in magenta (AxNiR numbering). The teal NO and magenta O2 ligands in the SRX models both occupy a similar binding mode apical to the T2Cu, while the blue O2 ligating the SF-ROX structure is shifted significantly towards the two catalytic residues in an end-on mode. (b) A comparison of SRX AxNiR, SF-ROX AxNiR and SFX AfNiR resting-state T2Cu sites. The AxNiR SRX structure is shown in red, the AxNiR SF-ROX structure in blue and the AfNiR SFX structure in green (Fukuda et al., 2016BB15). The simulated-annealing Fo − Fc OMIT electron-density maps are superimposed on the oxygen and water ligands contoured at 6σ in green and red meshes, respectively. The SFX AfNiR resting-state T2Cu is bound by chloride ion from purification that is bound asymmetrically with respect to the His3 plane.

IUCrJ
Volume 5| Part 1| January 2018| Pages 22-31
ISSN: 2052-2525
https://doi.org/10.1107/S2052252517016128