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Journal of Bacteriology, May 2003, p. 2952-2960, Vol. 185, No. 9
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.9.2952-2960.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

The Cell Wall of the Pathogenic Bacterium Rhodococcus equi Contains Two Channel-Forming Proteins with Different Properties

Franziska G. Rieß,1 Marion Elflein,1 Michael Benk,1 Bettina Schiffler,1 Roland Benz,1* Natalie Garton,2 and Iain Sutcliffe2

Lehrstuhl für Biotechnologie, Biozentrum der Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany,1 University of Sunderland, Institute of Pharmacy, Fleming Building, Sunderland SR2 3SD, England2

Received 2 December 2002/ Accepted 12 February 2003

We have identified in organic solvent extracts of whole cells of the gram-positive pathogen Rhodococcus equi two channel-forming proteins with different and complementary properties. The isolated proteins were able to increase the specific conductance of artificial lipid bilayer membranes made from phosphatidylcholine-phosphatidylserine mixtures by the formation of channels able to be permeated by ions. The channel-forming protein PorAReq (R. equi pore A) is characterized by the formation of cation-selective channels, which are voltage gated. PorAReq has a single-channel conductance of 4 nS in 1 M KCl and shows high permeability for positively charged solutes because of the presence of negative point charges. According to the results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the protein has an apparent molecular mass of about 67 kDa. The analysis (using the effect of negative charges on channel conductance) of the concentration dependence of the single-channel conductance suggested that the diameter of the cell wall channel is about 2.0 nm. The second channel (formed by PorBReq [R. equi pore B]) shows a preferred movement of anions through the channel and is not voltage gated. This channel shows a single-channel conductance of 300 pS in 1 M KCl and is characterized by the presence of positive point charges in or near the channel mouth. Based on SDS-PAGE, the apparent molecular mass of the channel-forming protein is about 11 kDa. Channel-forming properties of the investigated cell wall porins were compared with those of others isolated from mycolic acid-containing actinomycetes. We present here the first report of a fully characterized anion-selective cell wall channel from a member of the order Actinomycetales.

* Corresponding author. Mailing address: Lehrstuhl für Biotechnologie, Biozentrum der Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany. Phone: 49 (0) 931-888-4501. Fax: 49 (0) 931-888-4509. E-mail: roland.benz{at}mail.uni-wuerzburg.de.

Journal of Bacteriology, May 2003, p. 2952-2960, Vol. 185, No. 9
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.9.2952-2960.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Nikaido, H. (2003). Molecular Basis of Bacterial Outer Membrane Permeability Revisited. Microbiol. Mol. Biol. Rev. 67: 593-656 [Abstract] [Full Text]  


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