Aquaporin-0 membrane junctions reveal the structure of a closed water pore.
The lens-specific water pore aquaporin-0 (AQP0) is the only aquaporin known to form membrane junctions in vivo. We show here that AQP0 from the lens core, containing some carboxy-terminally cleaved AQP0, forms double-layered crystals that recapitulate in vivo junctions. We present the structure of the AQP0 membrane junction as determined by electron crystallography. The junction is formed by three localized interactions between AQP0 molecules in adjoining membranes, mainly mediated by proline residues conserved in AQP0s from different species but not present in most other aquaporins. Whereas all previously determined aquaporin structures show the pore in an open conformation, the water pore is closed in AQP0 junctions. The water pathway in AQP0 also contains an additional pore constriction, not seen in other known aquaporin structures, which may be responsible for pore gating.
Gonen
Tamir
T
Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA.
Sliz
Piotr
P
Kistler
Joerg
J
Cheng
Yifan
Y
Walz
Thomas
T
D000818:Animals; D020346:Aquaporins; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D002463:Cell Membrane Permeability; D020285:Cryoelectron Microscopy; D003460:Crystallization; D004553:Electric Conductivity; D005136:Eye Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism / Q000648:ultrastructure*; D006863:Hydrogen-Ion Concentration; D007908:Lens, Crystalline / Q000737:chemistry; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism / Q000648:ultrastructure*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D012756:Sheep; D014867:Water / Q000378:metabolism
D020346:Aquaporins; D005136:Eye Proteins; D008562:Membrane Glycoproteins; C030328:aquaporin 0; D014867:Water