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Archives of Microbiology

, Volume 171, Issue 3, pp 173–182 | Cite as

The cell wall porin of the gram-positive bacterium Nocardia asteroides forms cation-selective channels that exhibit asymmetric voltage dependence

  • Franziska G. Rieß
  • Thomas Lichtinger
  • Atteyet F. Yassin
  • Klaus P. Schaal
  • R. Benz
Original paper

Abstract

Detergent-solubilized cell wall extracts of the gram-positive, strictly aerobic bacterium Nocardia asteroides contain channel-forming activity as judged from reconstitution experiments using lipid bilayer membranes. The cell wall porin was identified as a protein with an apparent molecular mass of about 84 kDa based on SDS-PAGE. The porin was purified to homogeneity using preparative SDS-PAGE. The 84-kDa protein was no longer observed after heating in SDS buffer. The presumed dissociation products were not observed on SDS-polyacrylamide gels. The cell wall porin increased the specific conductance of artificial lipid bilayer membranes from phosphatidylcholine/phosphatidylserine mixtures by the formation of cation-selective channels, which had an average single-channel conductance of 3.0 nS in 1 M KCl. The single-channel conductance was only moderately dependent on the bulk aqueous KCl concentration, which indicated negative point charge effects on the channel properties. The analysis of the concentration dependence of the single-channel conductance using the effect of negative charges on channel conductance suggested that the diameter of the cell wall channel is about 1.4 nm. Asymmetric addition of the cell wall porin to lipid bilayer membranes resulted in an asymmetric voltage dependence. The cell wall channel switched into substates, when the cis side of the membrane, the side of the addition of the protein, had negative polarity. Positive potentials at the cis side had no influence on the conductance of the cell wall channel.

Key words Cell wall channel Mycolic acid Porin Nocardia asteroides Lipid bilayer membrane 

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Copyright information

© Springer-Verlag Berlin Heidelberg 1999

Authors and Affiliations

  • Franziska G. Rieß
    • 1
  • Thomas Lichtinger
    • 1
  • Atteyet F. Yassin
    • 2
  • Klaus P. Schaal
    • 2
  • R. Benz
    • 1
  1. 1.Lehrstuhl für Biotechnologie, Biozentrum der Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany e-mail: roland.benz@mail.uni-wuerzburg.de Tel. +49-931-888-4501; Fax +49-931-888-4509DE
  2. 2.Institut für Medizinische Mikrobiologie und Immunologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Sigmund-Freud-Strasse 25, D-53105 Bonn, GermanyDE

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