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Porin channel triplets merge into single outlets in Escherichia coli outer membranes

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Abstract

Previous observations on the structural1–4 and functional5 properties of porin, the matrix protein of Escherichia coli, have indicated that the channel-forming trimers span the outer membranes of the bacterial cell, forming a molecular sieve6. By using electron microscopy and image reconstruction, we demonstrate here that three channels on the outer surface of the cell merge into a single channel at the periplasmic face. Conductance measurements using conditions under which single activated triplets could be observed led us to conclude that the three individual consecutive closing steps reflect three channels within a single trimeric unit. Statistical analysis of conductance levels revealed that the first relaxation step is distinctly smaller than the two subsequent channel closings. This functional observation can be explained if the channels of porin trimers coalesce.

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Authors and Affiliations

  1. Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056, Basel, Switzerland

    A. Engel, A. Massalski, H. Schindler & J. P. Rosenbusch

  2. Medical Foundation of Buffalo, 73 High Street, Buffalo, New York, 14243, USA

    D. L. Dorset

  3. European Molecular Biology Laboratory, PO Box 10.2209, D-6900, Heidelberg, FRG

    J. P. Rosenbusch

Authors
  1. A. Engel
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  2. A. Massalski
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  3. H. Schindler
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  4. D. L. Dorset
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  5. J. P. Rosenbusch
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Engel, A., Massalski, A., Schindler, H. et al. Porin channel triplets merge into single outlets in Escherichia coli outer membranes. Nature 317, 643–645 (1985). https://doi.org/10.1038/317643a0

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  • DOI: https://doi.org/10.1038/317643a0

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