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Figure 4
Hydrogen-bond network at the T2Cu active-site pocket. The primary proton channel (PPC) is blocked by Ile221 in TsNirK and the secondary proton channel (SPC) is accessed from the bulk solution. The contribution of subunit A and the subunit C to build the external surface and the channel mouth are indicated in magenta and yellow, respectively (inset). Residues that build the sensing loop (red), the Cys–His bridge (green) and the amino-acid chain from ValCAT to Phe222 (orange) are indicated. A hydrogen-bond network is built by several water molecules from the mouth of the channel to the T2Cu active site (in red) and a chain of occluded water molecules (in magenta). The occluded water molecules connect SerCAT to HisCAT via Gln239 and Thr240. Thr86 and Ser87 link the water chains. Ala116, Leu77, Gly91 and Asn92 are involved in the hydrogen-bond network towards the protein surface.

IUCrJ
Volume 6| Part 2| March 2019| Pages 248-258
ISSN: 2052-2525
https://doi.org/10.1107/S2052252519000241