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PDBsum entry 2f1c
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Membrane protein
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PDB id
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2f1c
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References listed in PDB file
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Key reference
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Title
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Crystal structure of the monomeric porin ompg.
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Authors
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G.V.Subbarao,
B.Van den berg.
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Ref.
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J Mol Biol, 2006,
360,
750-759.
[DOI no: ]
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PubMed id
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Abstract
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The outer membrane (OM) of Gram-negative bacteria contains a large number of
channel proteins that mediate the uptake of ions and nutrients necessary for
growth and functioning of the cell. An important group of OM channel proteins
are the porins, which mediate the non-specific, diffusion-based passage of small
(<600 Da) polar molecules. All porins of Gram-negative bacteria that have
been crystallized to date form stable trimers, with each monomer composed of a
16-stranded beta-barrel with a relatively narrow central pore. In contrast, the
OmpG porin is unique, as it appears to function as a monomer. We have determined
the X-ray crystal structure of OmpG from Escherichia coli to a resolution of 2.3
A. The structure shows a 14-stranded beta-barrel with a relatively simple
architecture. Due to the absence of loops that fold back into the channel, OmpG
has a large ( approximately 13 A) central pore that is considerably wider than
those of other E. coli porins, and very similar in size to that of the toxin
alpha-hemolysin. The architecture of the channel, together with previous
biochemical and other data, suggests that OmpG may form a non-specific channel
for the transport of larger oligosaccharides. The structure of OmpG provides the
starting point for engineering studies aiming to generate selective channels and
for the development of biosensors.
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Figure 3.
Figure 3. Architecture of the OmpG pore. (a) Stereo
backbone representation of OmpG in a direction perpendicular to
the membrane and viewed from the extracellular side, showing the
charged and aromatic residues in the pore constriction, with
2F[o] – F[c] electron density for the side-chains in blue,
contoured at 1.2 σ. Residue numbers are indicated. (b) Surface
representations of the OmpG channel viewed from the
extracellular side (left, orientation similar to that in (a))
and the periplasmic side (right), showing the electrostatic
surface potentials inside the channel. The surface is colored
blue for potentials > 15 kT/e and red for potentials < –15
kT/e. The Figure was generated with GRASP.^38
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Figure 5.
Figure 5. Stereo backbone representation of E. coli OmpG
from the extracellular side, showing the distribution of
aromatic (grey) and charged residues (red, glutamic acid
15/17/31/52/152/174; blue, arginine 68/92/111/150) on the
extracellular side of the constriction. The numbers of the
aromatic residues (Y50, F66, Y94, Y96, Y98, F132, Y136 and Y146)
that may provide binding sites for oligosaccharides are
indicated. For clarity, the barrel has been tilted and only
residues present on one side of the constriction are shown.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2006,
360,
750-759)
copyright 2006.
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