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PDBsum entry 1osm
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Outer membrane protein
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PDB id
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1osm
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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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Crystal structure and functional characterization of ompk36, The osmoporin of klebsiella pneumoniae.
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Authors
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R.Dutzler,
G.Rummel,
S.Albertí,
S.Hernández-Allés,
P.Phale,
J.Rosenbusch,
V.Benedí,
T.Schirmer.
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Ref.
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Structure, 1999,
7,
425-434.
[DOI no: ]
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PubMed id
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Abstract
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BACKGROUND: Porins are channel-forming membrane proteins that confer solute
permeability to the outer membrane of Gram-negative bacteria. In Escherichia
coli, major nonspecific porins are matrix porin (OmpF) and osmoporin (OmpC),
which show high sequence homology. In response to high osmolarity of the medium,
OmpC is expressed at the expense of OmpF porin. Here, we study osmoporin of the
pathogenic Klebsiella pneumoniae (OmpK36), which shares 87% sequence identity
with E. coliOmpC in an attempt to establish why osmoporin is best suited to
function at high osmotic pressure. RESULTS: The crystal structure of OmpK36 has
been determined to a resolution of 3.2 A by molecular replacement with the model
of OmpF. The structure of OmpK36 closely resembles that of the search model. The
homotrimeric structure is composed of three hollow 16-stranded antiparallel beta
barrels, each delimiting a separate pore. Most insertions and deletions with
respect to OmpF are found in the loops that protrude towards the cell exterior.
A characteristic ten-residue insertion in loop 4 contributes to the subunit
interface. At the pore constriction, the replacement of an alanine by a tyrosine
residue does not alter the pore profile of OmpK36 in comparison with OmpF
because of the different course of the mainchain. Functionally, as characterized
in lipid bilayers and liposomes, OmpK36 resembles OmpC with decreased
conductance and increased cation selectivity in comparison with OmpF.
CONCLUSIONS: The osmoporin structure suggests that not an altered pore size but
an increase in charge density is the basis for the distinct physico-chemical
properties of this porin that are relevant for its preferential expression at
high osmotic strength.
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Figure 3.
Figure 3. Cyclic-averaged electron-density map (contoured
at 1s) of OmpK36. (a) Stereoview of the OmpK36 pore viewed from
the extracellular side. Residues of the arginine cluster are
labeled (OmpF numbering convention). The internal loop L3 is
seen at the right side of the pore. (b) Stereoview of the
extracellular loop L4 (with carbon atoms coloured in yellow),
which interacts with loop L1 (carbon atoms coloured in white) of
a neighbouring monomer. Figures were generated with the program
DINO (Philippsen, 1998; http://www.bioz.unibas.ch/ not, vert,
similar- xray/dino).
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The above figure is
reprinted
by permission from Cell Press:
Structure
(1999,
7,
425-434)
copyright 1999.
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