Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 389, Issue 4, Pages 694-706Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2009.04.049
Keywords
water channel; electron crystallography; fast water selective mechanism; cell adhesion; glial lamellae
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Funding
- Japan New Energy and Tndustrial Technology Development Organization
- Japan Society for the Promotion of Science
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Members of the aquaporin (AQP) family are expressed in almost every organism, including 13 homologues in humans. Based on the electron crystallographic structure of AQP1, the hydrogen-bond isolation mechanism was proposed to explain why AQPs are impermeable to protons despite their very fast water conduction. The mechanism by which AQPs exclude protons remained controversial, however. Here we present the structure of AQP4 at 2.8 angstrom resolution obtained by electron crystallography of double-layered two-dimensional crystals. The resolution has been improved from the previous 3.2 angstrom, with accompanying improvement in data quality resulting in the ability to identify individual water molecules. Our structure of AQP4, the predominant water channel in the brain, reveals eight water molecules in the channel. The arrangement of the waters provides support for the hydrogen-bond isolation mechanism. Our AQP4 structure also visualizes five lipids, showing that direct interactions of the extracellular surface of AQP4 with three lipids in the adjoining membrane help stabilize the membrane junction. (C) 2009 Elsevier Ltd. All rights reserved.
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