Crystal structure of Omp32, the anion-selective porin from Comamonas acidovorans, in complex with a periplasmic peptide at 2.1 Å resolution

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2000
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Zeth, Kornelius
Engelhardt, Harald
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Structure ; 8 (2000), 9. - pp. 981-992. - ISSN 0969-2126
Abstract
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 Å using single isomorphous replacement with anomalous scattering (SIRAS). The porin consists of a 16-stranded β barrel with eight external loops and seven periplasmic turns. Loops 3 and 8, together with a protrusion located within β-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 β-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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570 Biosciences, Biology
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anion-selective ion channel,electrophysiology,outer membrane protein,porin Omp32,X-ray structure
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ISO 690ZETH, Kornelius, Kay DIEDERICHS, Wolfram WELTE, Harald ENGELHARDT, 2000. Crystal structure of Omp32, the anion-selective porin from Comamonas acidovorans, in complex with a periplasmic peptide at 2.1 Å resolution. In: Structure. 8(9), pp. 981-992. ISSN 0969-2126. Available under: doi: 10.1016/S0969-2126(00)00189-1
BibTex
@article{Zeth2000Cryst-8370,
  year={2000},
  doi={10.1016/S0969-2126(00)00189-1},
  title={Crystal structure of Omp32, the anion-selective porin from Comamonas acidovorans, in complex with a periplasmic peptide at 2.1 Å resolution},
  number={9},
  volume={8},
  issn={0969-2126},
  journal={Structure},
  pages={981--992},
  author={Zeth, Kornelius and Diederichs, Kay and Welte, Wolfram and Engelhardt, Harald}
}
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