title: Structural basis of water-specific transport through the AQP1 water channel.
abstract: Water channels facilitate the rapid transport of water across cell membranes in response to osmotic gradients. These channels are believed to be involved in many physiological processes that include renal water conservation, neuro-homeostasis, digestion, regulation of body temperature and reproduction. Members of the water channel superfamily have been found in a range of cell types from bacteria to human. In mammals, there are currently 10 families of water channels, referred to as aquaporins (AQP): AQP0-AQP9. Here we report the structure of the aquaporin 1 (AQP1) water channel to 2.2 A resolution. The channel consists of three topological elements, an extracellular and a cytoplasmic vestibule connected by an extended narrow pore or selectivity filter. Within the selectivity filter, four bound waters are localized along three hydrophilic nodes, which punctuate an otherwise extremely hydrophobic pore segment. This unusual combination of a long hydrophobic pore and a minimal number of solute binding sites facilitates rapid water transport. Residues of the constriction region, in particular histidine 182, which is conserved among all known water-specific channels, are critical in establishing water specificity. Our analysis of the AQP1 pore also indicates that the transport of protons through this channel is highly energetically unfavourable.
authors.affiliation: Life Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720, USA.
authors.forename: H
authors.initials: H
authors.lastname: Sui
authors.forename: B G
authors.initials: BG
authors.lastname: Han
authors.forename: J K
authors.initials: JK
authors.lastname: Lee
authors.forename: P
authors.initials: P
authors.lastname: Walian
authors.forename: B K
authors.initials: BK
authors.lastname: Jap
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D051398:Aquaporin 1; D020346:Aquaporins / Q000737:chemistry* / Q000378:metabolism; D001692:Biological Transport; D001789:Blood Group Antigens; D018360:Crystallography, X-Ray; D006801:Humans; D017136:Ion Transport; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D014867:Water / Q000378:metabolism*
chemical_list: C496020:AQP1 protein, human; D020346:Aquaporins; D001789:Blood Group Antigens; D014867:Water; D051398:Aquaporin 1