1. Department of Cell Biology and
2. Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA
3. Howard Hughes Medical Institute and Children's Hospital Laboratory of Molecular Medicine, 320 Longwood Avenue, Boston, Massachusetts 02115, USA
4. Department of Biophysics, Kyoto University, Oiwake, Kitashirakawa Sakyo-ku, Kyoto 606-8502, Japan

Correspondence to: Thomas Walz¹ Correspondence and requests for materials should be addressed to T.W. (Email: twalz@hms.harvard.edu). Coordinates and structure factors for junctional and nonjunctional AQP0 have been deposited in the Protein Data Bank (accession codes 2B6O and 2B6P, respectively).

Abstract

Lens-specific aquaporin-0 (AQP0) functions as a specific water pore and forms the thin junctions between fibre cells. Here we describe a 1.9 Å resolution structure of junctional AQP0, determined by electron crystallography of double-layered two-dimensional crystals. Comparison of junctional and non-junctional AQP0 structures shows that junction formation depends on a conformational switch in an extracellular loop, which may result from cleavage of the cytoplasmic amino and carboxy termini. In the centre of the water pathway, the closed pore in junctional AQP0 retains only three water molecules, which are too widely spaced to form hydrogen bonds with each other. Packing interactions between AQP0 tetramers in the crystalline array are mediated by lipid molecules, which assume preferred conformations. We were therefore able to build an atomic model for the lipid bilayer surrounding the AQP0 tetramers, and we describe lipid–protein interactions.

1. Department of Cell Biology and
2. Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA
3. Howard Hughes Medical Institute and Children's Hospital Laboratory of Molecular Medicine, 320 Longwood Avenue, Boston, Massachusetts 02115, USA
4. Department of Biophysics, Kyoto University, Oiwake, Kitashirakawa Sakyo-ku, Kyoto 606-8502, Japan

Correspondence to: Thomas Walz¹ Correspondence and requests for materials should be addressed to T.W. (Email: twalz@hms.harvard.edu). Coordinates and structure factors for junctional and nonjunctional AQP0 have been deposited in the Protein Data Bank (accession codes 2B6O and 2B6P, respectively).

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