Lipid molecules nestle into specific hydrophobic grooves on outside of aquaporin-0 tetramers. Adapted from Supplementary Figure 6 by Lee AG (2005) Nature 438, 569-570.

Specific lipid-protein interactions can be visualized in the structure of two-dimensional Aquaporin-0 crystals as determined by cryoelectron microscopy ("cryo em") at the remarkable resolution of 1.9 Angstroms.
Tamir Gonen, now an Assistant Professor of Biochemistry, recently completed this work as a postdoctoral fellow with Professors Thomas Walz and Stephen Harrison at Harvard Medical School. The article is Gonen T, Cheng Y, Sliz P, Hiroaki Y, Fujiyoshi Y, Harrison SC, Walz T (2005) Lipid-protein interactions in double-layered two-dimensional AQP0 crystals. Nature 438, 633-638. Also see News and Views by Lee AG (2005) A greasy grip. Nature 438, 569-570. The previous article in this series was Gonen T, Sliz P, Kistler J, Cheng Y, Walz T (2004) Aquaporin-0 membrane junctions reveal the structure of a closed water pore. Nature 429, 193-197.

Abstract

Lens-specific aquaporin-0 (AQP0) functions as a specific water pore and forms the thin junctions between fibre cells. Here we describe a 1.9Å 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.