title: Projection structure of the CHIP28 water channel in lipid bilayer membranes at 12-A resolution.
abstract: Osmotic water transport across plasma membranes in erythrocytes and several epithelial cell types is facilitated by CHIP28, a water-selective membrane channel protein. In order to examine the structure of CHIP28 in membranes, large (1.5-2.5-microns diameter), highly ordered, two-dimensional (2-D) crystals of purified and deglycosylated erythrocyte CHIP28 were generated by reconstitution of detergent-solubilized protein into synthetic lipid bilayers via detergent dialysis. Fourier transforms computed from low-dose electron micrographs of such crystals preserved in negative stain display order to 12-A resolution. The crystal lattice is tetragonal (a = b = 99.2 +/- 1.4 A) with plane group symmetry p4g. A projection density map at 12-A resolution defines the molecular boundary and organization of the CHIP28 monomers in the membrane plane. The unit cell contains four CHIP28 dimers, each composed of two oblong-shaped (37 x 25 A ) monomers with opposite orientations. The CHIP28 monomers associate to form tetrameric structures around the 4-fold axes normal to the membrane plane where stain is excluded. The 2-D crystals of CHIP28 display order extending beyond the limit typically achieved by negative staining and therefore may be amenable to high-resolution structure analysis by cryo-electron microscopy.
authors.affiliation: Department of Cell Biology, Scripps Research Institute, La Jolla, California.
authors.forename: A K
authors.initials: AK
authors.lastname: Mitra
authors.forename: M
authors.initials: M
authors.lastname: Yeager
authors.forename: A N
authors.initials: AN
authors.lastname: van Hoek
authors.forename: M C
authors.initials: MC
authors.lastname: Wiener
authors.forename: A S
authors.initials: AS
authors.lastname: Verkman
mesh_terms: D051398:Aquaporin 1; D020346:Aquaporins; D001789:Blood Group Antigens; D003460:Crystallization; D005583:Fourier Analysis; D006031:Glycosylation; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007473:Ion Channels / Q000097:blood / Q000737:chemistry* / Q000648:ultrastructure; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D046911:Macromolecular Substances; D008854:Microscopy, Electron
chemical_list: C496020:AQP1 protein, human; D020346:Aquaporins; D001789:Blood Group Antigens; D007473:Ion Channels; D008051:Lipid Bilayers; D008081:Liposomes; D046911:Macromolecular Substances; D051398:Aquaporin 1