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PDBsum entry 2fcp
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Membrane protein
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PDB id
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2fcp
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Siderophore-Mediated iron transport: crystal structure of fhua with bound lipopolysaccharide.
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Authors
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A.D.Ferguson,
E.Hofmann,
J.W.Coulton,
K.Diederichs,
W.Welte.
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Ref.
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Science, 1998,
282,
2215-2220.
[DOI no: ]
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PubMed id
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Abstract
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FhuA, the receptor for ferrichrome-iron in Escherichia coli, is a member of a
family of integral outer membrane proteins, which, together with the
energy-transducing protein TonB, mediate the active transport of ferric
siderophores across the outer membrane of Gram-negative bacteria. The
three-dimensional structure of FhuA is presented here in two conformations: with
and without ferrichrome-iron at resolutions of 2.7 and 2.5 angstroms,
respectively. FhuA is a beta barrel composed of 22 antiparallel beta strands. In
contrast to the typical trimeric arrangement found in porins, FhuA is monomeric.
Located within the beta barrel is a structurally distinct domain, the
"cork," which mainly consists of a four-stranded beta sheet and four
short alpha helices. A single lipopolysaccharide molecule is noncovalently
associated with the membrane-embedded region of the protein. Upon binding of
ferrichrome-iron, conformational changes are transduced to the periplasmic
pocket of FhuA, signaling the ligand-loaded status of the receptor. Sequence
homologies and mutagenesis data are used to propose a structural mechanism for
TonB-dependent siderophore-mediated transport across the outer membrane.
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Figure 3.
Fig. 3. Representative section of the electron density map.
Stereoview of the final 3F[obs]-2F[calc] electron density map
(blue) at a resolution of 2.7 Å is contoured at 1.5  , showing
the ferrichrome-iron binding site, including water molecules.
The ferrichrome-iron molecule is shown in yellow, and the iron
atom is indicated as a large red sphere. Select side-chain
residues (Glu98, Gly99, and Gln100 from apex B; Tyr116 from apex
C; Tyr244 and Trp246 from L3; Phe^313 from  7; Phe^391
from 9; and
Phe^702 from 21) and the
two water molecules (Wat151 and Wat154) found in the binding
site are labeled (34) and colored white and red, respectively.
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Figure 4.
Fig. 4. Conformational changes induced upon ferrichrome-iron
binding. Superposition of the  -carbon
coordinates of FhuA and its complex with ferrichrome-iron
illustrating the ligand-induced conformational changes observed
in the cork domain. The cork domains of FhuA and its complex
with ferrichrome-iron are shown in purple and yellow,
respectively. The barrel strands (shown in blue) are represented
as thin lines for clarity of the cork domain. Apices A, B, and C
and Glu19 are labeled (34).
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The above figures are
reprinted
by permission from the AAAs:
Science
(1998,
282,
2215-2220)
copyright 1998.
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