Abstract
We studied the channel formed by the mycobacterial porin from the cell wall of Mycobacterium chelonae (Trias, J., Jarlier, V., and Benz, R. (1992) Science 258, 1479-1481) by reconstituting the mycobacterial porin and cell wall extracts in lipid bilayer membranes. The channel exhibited two different states in lipid bilayer membranes at 10 mV of applied voltage. One was characterized by a steplike appearance while the other showed a fast, voltage-dependent, flickering behavior between a closed and an open state. The channel was voltage-gated, and starting at 40 mV of applied voltage the mycobacterial porin channel switched to a closed configuration in an asymmetric fashion. The channel was cation-selective and had 2.5-point negative charges at both sides of the channel. Identical channels were observed when membranes were reconstituted with cell wall extracts, suggesting that there is only one porin species in the mycobacterial cell wall.
Highlights
From the $Luboratoire de Bacteriologie-Virologie, Faculte de Medecine Pit@-SalpftrGre,75634Paris Cedex 13, France, and lILehrstuh1fur Bwtechnologie, Universitiit Wurzburg, Biozentrum, A m Hubland, 0-8700Wurzburg, Federal Republic of Germany
We studied the channel formed by the mycobacterialalyer which would beformed by the mycolates that arebound porin from the cell wall of Mycobacterium chelonae to the arabinogalactan molecules and the free lipids (2, 4)
268, 1479-1481) by reconstituting the mycobacterial permeability barrier, and it is commonly believed that this bwophwTtioahaalhravesseiyicnrocvehhrorasaalhnmtnrboanadeewcgectmeelwteele-dlbxgerwhreiazaaniatfbenealdildestaeset,bx,daayvctntrlodoaa1lstscs0taettwtdegsampeiornV-latdiidknneoliedipfgfpfaeeaiadpnarptnpdeps4nebelt0aintoiaelrtpatdsma,eyetfn.alVvneiTctroceehklostwemfearaihgnecipeinmlhlp.iegpalbOibntierdhnendaee-enlespbhhoi.nrfaauturstrmrheusi,aceehneMropllwieypusrcalnmraot,ehrbeiseonaapgctbogoteineolnarisotiiidycwubmlaoimedgftefruytoehbrceraoeemntrbhccgaeeueecnllltitooenwfwsrtiiaarsiainlt,nlhtssiouobtifhccriMoehrMtseyieacsycsiscmos.obtMoTabadnaychecccteeleotsermb,iroautifehucmaimtamsetcurhpirauteeovhmlmrioetucnaemleannele-tt-l voltage the mycobacterial porin channel switched to awall acts as amolecular sieve and is an efficient permeability closed configuration in an asymmetric fashion
Summary
From the $Luboratoire de Bacteriologie-Virologie, Faculte de Medecine Pit@-SalpftrGre,75634Paris Cedex 13, France, and lILehrstuh1fur Bwtechnologie, Universitiit Wurzburg, Biozentrum, A m Hubland, 0-8700Wurzburg, Federal Republic of Germany. We studied the channel formed by the mycobacterialalyer which would beformed by the mycolates that arebound porin from the cell wall of Mycobacterium chelonae to the arabinogalactan molecules and the free lipids (2, 4). Like other Gram-positive bacteria it contains a thick conventional peptidoglycan sacculus that surrounds the cytoplasmic membrane and prevents the bacteria from osmotic lysis. It contains proteins and lipopolysaccharide molecules, and it is extremely rich in lipids that can account for up to 60% of the cell wall weight(1-3). The main cell wall component is a matrix formed by the peptidoglycan which is covalently linked to arabinogalactan molecules that are esterified to mycolic acids (high molecular weight a-alkyl, phydroxy fatty acids). Despite the low permeability of the cell wall, the penetration of these compounds into the cell takes place mainly in a hydrophilic environment (5), which suggests the presence of defined hydrophilic pathways in the cell wall of mycobacteria
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