title: Structure of the major membrane protein complex from urinary bladder epithelial cells by cryo-electron crystallography.
abstract: Numerous protein plaques cover the apical surface of mammalian urinary bladder epithelial cells. These plaques contain four integral membrane proteins, called uroplakins, which form a well-ordered array of hexameric complexes. The 3D structure of these naturally occurring 2D crystals was studied by cryo-electron-crystallographic methods using a slow-scan charged-coupled device (CCD) camera to record the electron micrographs. A 1.2 nm projection map calculated from untilted crystals shows that each hexamer comprises a ring of six inner and six outer domains at a radius of 5.7 nm and 9.2 nm respectively. The 3D structure shows that the mass is distributed strongly asymmetrically with respect to the membrane, with most of the mass protruding from the luminal face. Both domains in the asymmetric unit traverse the membrane and protrude from the membrane on the cytoplasmic side. On the luminal side, the two domains are bridged forming a stretched arc. The total thickness of the complex is about 13.2 nm. A model of the urothelial plaque reveals that contacts between the hexamers are much less extended than within the hexamers.
authors.affiliation: Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, AG Groningen, NL-9747, The Netherlands. oostergetel@chem.rug.nl
authors.forename: G T
authors.initials: GT
authors.lastname: Oostergetel
authors.forename: W
authors.initials: W
authors.lastname: Keegstra
authors.forename: A
authors.initials: A
authors.lastname: Brisson
mesh_terms: D000686:Amyloidosis / Q000378:metabolism; D000818:Animals; D020285:Cryoelectron Microscopy; D003460:Crystallization; D004847:Epithelial Cells / Q000737:chemistry* / Q000648:ultrastructure; D005583:Fourier Analysis; D005615:Freezing; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D051379:Mice; D008958:Models, Molecular; D008970:Molecular Weight; D020836:Protein Structure, Quaternary; D059470:Tetraspanins; D001743:Urinary Bladder / Q000737:chemistry* / Q000166:cytology / Q000648:ultrastructure; D060170:Uroplakin II; D060171:Uroplakin III; D060167:Uroplakin Ia; D060169:Uroplakin Ib
chemical_list: D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D059470:Tetraspanins; C086452:UPK1B protein, human; C554658:UPK2 protein, human; C490123:Upk1a protein, mouse; C490124:Upk1b protein, mouse; C554659:Upk2 protein, mouse; D060170:Uroplakin II; D060171:Uroplakin III; D060167:Uroplakin Ia; D060169:Uroplakin Ib