title: The structure of aquaporin-1 at 4.5-A resolution reveals short alpha-helices in the center of the monomer.
abstract: Aquaporin-1 is a water channel found in mammalian red blood cells that is responsible for high water permeability of its membrane. Our electron crystallographic analysis of the three-dimensional structure of aquaporin-1 at 4.5-A resolution confirms the previous finding that each subunit consists of a right-handed bundle of six highly tilted transmembrane helices that surround a central X-shaped structure. In our new potential map, the rod-like densities for the transmembrane helices show helically arranged protrusions, indicating the positions of side chains. Thus, in addition to the six transmembrane helices, observation of helically arranged side-chain densities allowed the identification of two short alpha-helices representing the two branches of the central X-shaped structure that extend to the extracellular and cytoplasmic membrane surfaces. The other two branches are believed to be loops connecting the short alpha-helix to a neighboring transmembrane helix. A pore found close to the center of the aquaporin-1 monomer is suggested to be the course of water flow with implications for the water selectivity.
authors.affiliation: Faculty of Science, Kyoto University, Kyoto, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Mitsuoka
authors.forename: K
authors.initials: K
authors.lastname: Murata
authors.forename: T
authors.initials: T
authors.lastname: Walz
authors.forename: T
authors.initials: T
authors.lastname: Hirai
authors.forename: P
authors.initials: P
authors.lastname: Agre
authors.forename: J B
authors.initials: JB
authors.lastname: Heymann
authors.forename: A
authors.initials: A
authors.lastname: Engel
authors.forename: Y
authors.initials: Y
authors.lastname: Fujiyoshi
mesh_terms: D051398:Aquaporin 1; D020346:Aquaporins / Q000737:chemistry*; D003461:Crystallography / Q000379:methods; D004583:Electrons; D004912:Erythrocytes / Q000737:chemistry; D007091:Image Processing, Computer-Assisted; D008565:Membrane Proteins / Q000737:chemistry; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D014867:Water / Q000737:chemistry
chemical_list: D020346:Aquaporins; D008565:Membrane Proteins; D014867:Water; D051398:Aquaporin 1