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Human aquaporin 1 (hAQP1) is the first discovered selective water channel present in lipid membranes of multiple types of cells. Several structures of hAQP1 and its bovine homolog have been obtained by electron microscopy and X-ray crystallography, giving a consistent picture of the transmembrane domain with the water-conducting pore. The transmembrane domain is formed by six full helices and two half-helices, which form a central constriction with conserved NPA motifs. Another constriction, ar/R filter, is found close to the extracellular surface, includes aromatic residues and a conserved arginine (Arg-195). While the existing crystal structures largely converge on the location of helical segments, they differ in details of conformation of the longest extracellular loop C and its interactions with the ar/R filter (in particular, with Arg-195). Here, we use solid-state Nuclear Magnetic Resonance to determine multiple interatomic distances, and come up with a refined structural model for hAQP1 which represents a physiologically relevant state predominant at non-cryogenic temperatures in a lipid environment. The model clearly disambiguates the position of Arg-195 sidechain disputed previously and shows a number of interactions for loop C, both with the ar/R filter and a number of other residues on the extracellular side of hAQP1.
This article was published in the following journal.
Name: The journal of physical chemistry. B
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