X-Message-Number: 15023
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Date: Sat, 25 Nov 2000 21:02:10 +0100 (CET)

Subject: Structure of a Glycerol-Conducting Channel and the Basis for Its 

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Structure of a Glycerol-Conducting Channel and the Basis for Its

Daxiong Fu, Andrew Libson, Larry J. W. Miercke, Cindy Weitzman, Peter
Nollert, Jolanta Krucinski, Robert M. Stroud*

Membrane channel proteins of the aquaporin family are highly selective
for permeation of specific small molecules, with absolute exclusion of
ions and charged solutes and without dissipation of the
electrochemical potential across the cell membrane. We report the
crystal structure of the Escherichia coli glycerol facilitator (GlpF)
with its primary permeant substrate glycerol at 2.2 angstrom
resolution. Glycerol molecules line up in an amphipathic channel in
single file. In the narrow selectivity filter of the channel the
glycerol alkyl backbone is wedged against a hydrophobic corner, and
successive hydroxyl groups form hydrogen bonds with a pair of
acceptor, and donor atoms. Two conserved aspartic acid-proline-alanine
motifs form a key interface between two gene-duplicated segments that
each encode three-and-one-half membrane-spanning helices around the
channel. This structure elucidates the mechanism of selective
permeability for linear carbohydrates and suggests how ions and water
are excluded.

Department of Biochemistry and Biophysics, School of Medicine,
University of California, San Francisco, CA 94143-0448, USA.

* To whom correspondence should be addressed. E-mail: 

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