Evidence for a small anion-selective channel in the cell wall of Mycobacterium bovis BCG besides a wide cation-selective pore

Two channels were observed in extracts of whole Mycobacterium bovis BCG cel ls using organic solvents and detergents. The channels derived from organic solvent treatment had a single-channel conductance of about 4.0 nS in 1 RI KCl in lipid bilayer membranes with properties similar to those of the cha nnels discovered previously in Mycobacterium smegmatis and Mycobacterium ch elonae. The channel was in its open configuration only at low transmembrane potentials. At higher voltages it switched to closed states that were almo st impermeable for ions. Lipid bilayer experiments in the presence of deter gent extracts of whole cells revealed another channel with a single-channel conductance of only 780 pS in 1 M KCI. Our results indicate that the mycol ic acid layer of M. Bovis BCG contains two channels, one is cation-selectiv e and its permeability properties can be finely controlled by cell mall asy mmetry or potentials. The other one is anion-selective, has a rather small single-channel conductance and is voltage-insensitive. The concentration of channel-forming proteins in the cell wall seems to be small, which is in a greement with the low cell wall permeability for hydrophilic salutes. (C) 1 999 Federation of European Biochemical Societies.