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Originally published In Press as doi:10.1074/jbc.M105045200 on July 9, 2001
J. Biol. Chem., Vol. 276, Issue 39, 36543-36549, September 28, 2001
Analysis of the Pore of the Unusual Major Intrinsic
Protein Channel, Yeast Fps1p*
Roslyn M.
Bill §,
Kristina
Hedfalk¶,
Sara
Karlgren ,
Jonathan G. L.
Mullins ,
Jan
Rydström**, and
Stefan
Hohmann 
From the Department of Cell and Molecular
Biology/Microbiology, Göteborg University, S-40530
Göteborg, Sweden, the ¶ Department of Molecular
Biotechnology, Chalmers University of Technology, S-40530
Göteborg, Sweden, the Department of Biology and Health
Science, University of Luton, Park Square, Luton, Bedfordshire, LU1
3JU, United Kingdom, and the ** Department of Biochemistry
and Biophysics, Göteborg University,
S-40530 Göteborg, Sweden
Fps1p is a glycerol efflux channel from
Saccharomyces cerevisiae. In this atypical major intrinsic
protein neither of the signature NPA motifs of the family, which
are part of the pore, is preserved. To understand the functional
consequences of this feature, we analyzed the pseudo-NPA motifs of
Fps1p by site-directed mutagenesis and assayed the resultant mutant
proteins in vivo. In addition, we took advantage of the
fact that the closest bacterial homolog of Fps1p, Escherichia
coli GlpF, can be functionally expressed in yeast, thus enabling
the analysis in yeast cells of mutations that make this typical major
intrinsic protein more similar to Fps1p. We observed that mutations
made in Fps1p to "restore" the signature NPA motifs did not
substantially affect channel function. In contrast, when GlpF was
mutated to resemble Fps1p, all mutants had reduced activity compared
with wild type. We rationalized these data by constructing models of
one GlpF mutant and of the transmembrane core of Fps1p. Our model
predicts that the pore of Fps1p is more flexible than that of GlpF. We
discuss the fact that this may accommodate the divergent NPA motifs of
Fps1p and that the different pore structures of Fps1p and GlpF may
reflect the physiological roles of the two glycerol facilitators.
*
This work was supported by European Commission Contracts
BIO4-CT98-0024 (to S. H. and J. R.) and FMRX-CT96-0128 (to
S. H.) and by a grant from the Carl Trygger Foundation (to J. R.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
§
To whom correspondence should be addressed. Tel:
46-31-773-3923; Fax: 46-31-773-2599; E-mail:
roslyn.bill@gmm.gu.se.

Special researcher supported by the Swedish Research Council.
Copyright © 2001 by The American Society for Biochemistry and Molecular Biology, Inc.

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Copyright © 2001 by the American Society for Biochemistry and Molecular Biology.
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