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Figure 10
Structure of human aquaporin 2 (hAQP2) obtained by room-temperature SFX from crystals directly grown on Roadrunner II chips. Views are parallel to the membrane plane (a) and perpendicular to the membrane plane (b) in cartoon representation. hAQP2 forms a homotetramer, with each monomer consisting of six transmembrane helices and two half-helices forming a pseudo-transmembrane helix. Each monomer is shown in a different color for clarity. Gray lines indicate the unit cell axes. (c) A water molecule (red sphere) is situated in the middle of the water channel of one monomer. The shown surface represents the solvent-excluded surface area viewed from the extracellular side. (d) The view perpendicular to the water channel shows that the water molecule is situated at a hydrogen-bond distance from the side chain of Asn68. This residue is part of the highly conserved dual NPA motif (pink and cyan) in the center of aquaporin channels that plays a central role in channel selectivity. The 2mFo − DFc electron density is shown at 0.8σ.

IUCrJ
Volume 6| Part 4| July 2019| Pages 714-728
ISSN: 2052-2525
https://doi.org/10.1107/S2052252519007395