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PDBsum entry 1e54
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Outer membrane protein
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PDB id
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1e54
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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 of omp32, The anion-Selective porin from comamonas acidovorans, In complex with a periplasmic peptide at 2.1 a resolution.
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Authors
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K.Zeth,
K.Diederichs,
W.Welte,
H.Engelhardt.
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Ref.
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Structure, 2000,
8,
981-992.
[DOI no: ]
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PubMed id
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Abstract
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BACKGROUND: Porins provide diffusion channels for salts and small organic
molecules in the outer membrane of bacteria. In OmpF from Escherichia coli and
related porins, an electrostatic field across the channel and a potential,
originating from a surplus of negative charges, create moderate cation
selectivity. Here, we investigate the strongly anion-selective porin Omp32 from
Comamonas acidovorans, which is closely homologous to the porins of pathogenic
Bordetella and Neisseria species. RESULTS: The crystal structure of Omp32 was
determined to a resolution of 2.1 A using single isomorphous replacement with
anomalous scattering (SIRAS). The porin consists of a 16-stranded beta barrel
with eight external loops and seven periplasmic turns. Loops 3 and 8, together
with a protrusion located within beta-strand 2, narrow the cross-section of the
pore considerably. Arginine residues create a charge filter in the constriction
zone and a positive surface potential at the external and periplasmic faces. One
sulfate ion was bound to Arg38 in the channel constriction zone. A peptide of
5.8 kDa appeared bound to Omp32 in a 1:1 stoichiometry on the periplasmic side
close to the symmetry axis of the trimer. Eight amino acids of this peptide
could be identified, revealing specific interactions with beta-strand 1 of the
porin. CONCLUSIONS: The Omp32 structure explains the strong anion selectivity of
this porin. Selectivity is conferred by a positive potential, which is not
attenuated by negative charges inside the channel, and by an extremely narrow
constriction zone. Moreover, Omp32 represents the anchor molecule for a peptide
which is homologous to proteins that link the outer membrane to the cell wall
peptidoglycan.
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Figure 5.
Figure 5. The surface of Omp32 oriented towards the outer
membrane. A girdle of ten lysine residues and one arginine is
enveloped by eight visible, oppositely charged aspartate
residues and one glutamate residue. The b strands are indicated
in yellow. The surface was calculated using the program MSMS
[51], and the representation was produced using the program DINO
(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
(2000,
8,
981-992)
copyright 2000.
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