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  • Title: Identification of a cell wall channel of Streptomyces griseus: the channel contains a binding site for streptomycin.
    Author: Kim BH, Andersen C, Benz R.
    Journal: Mol Microbiol; 2001 Aug; 41(3):665-73. PubMed ID: 11532134.
    Abstract:
    Cells of the Gram-positive actinomycete Streptomyces griseus were disrupted and the cell envelope was subjected to sucrose step-gradient centrifugation. The different fractions were analysed for NADH-oxidase activity and the formation of ion-permeable channels in lipid bilayers. Highest channel-forming activity and highest NADH-oxidase activity were found in different fractions. The cell wall fraction contained an ion-permeable channel with a single-channel conductance of 850 pS in 1 M KCl. The channel-forming protein, with an apparent molecular mass of 28 kDa, was purified to homogeneity using fast protein liquid chromatography after the extraction of whole cells with detergent. Single-channel experiments suggest that the cell wall channel is wide and water-filled. Titration experiments with streptomycin produced by S. griseus suggested that the cell wall channel binds this antibiotic with a half saturation constant of about 6 mM in 1 M KCl. The binding of streptomycin was found to be ionic strength dependent and the half saturation constant decreased to 60 microM at 0.1 M KCl. The results indicate that the 28 kDa protein represents the hydrophilic pathway through the cell wall of the Gram-positive bacterium S. griseus.
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