title: Cardiolipin controls the osmotic stress response and the subcellular location of transporter ProP in Escherichia coli.
abstract: The phospholipid composition of the membrane and transporter structure control the subcellular location and function of osmosensory transporter ProP in Escherichia coli. Growth in media of increasing osmolality increases, and entry to stationary phase decreases, the proportion of phosphatidate in anionic lipids (phosphatidylglycerol (PG) plus cardiolipin (CL)). Both treatments increase the CL:PG ratio. Transporters ProP and LacY are concentrated with CL (and not PG) near cell poles and septa. The polar concentration of ProP is CL-dependent. Here we show that the polar concentration of LacY is CL-independent. The osmotic activation threshold of ProP was directly proportional to the CL content of wild type bacteria, the PG content of CL-deficient bacteria, and the anionic lipid content of cells and proteoliposomes. CL was effective at a lower concentration in cells than in proteoliposomes, and at a much lower concentration than PG in either system. Thus, in wild type bacteria, osmotic induction of CL synthesis and concentration of ProP with CL at the cell poles adjust the osmotic activation threshold of ProP to match ambient conditions. ProP proteins linked by homodimeric, C-terminal coiled-coils are known to activate at lower osmolalities than those without such structures and coiled-coil disrupting mutations raise the osmotic activation threshold. Here we show that these mutations also prevent polar concentration of ProP. Stabilization of the C-terminal coiled-coil by covalent cross-linking of introduced Cys reverses the impact of increasing CL on the osmotic activation of ProP. Association of ProP C termini with the CL-rich membrane at cell poles may raise the osmotic activation threshold by blocking coiled-coil formation. Mutations that block coiled-coil formation may also block association of the C termini with the CL-rich membrane.
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
authors.forename: Tatyana
authors.initials: T
authors.lastname: Romantsov
authors.forename: Leanne
authors.initials: L
authors.lastname: Stalker
authors.forename: Doreen E
authors.initials: DE
authors.lastname: Culham
authors.forename: Janet M
authors.initials: JM
authors.lastname: Wood
mesh_terms: D000595:Amino Acid Sequence; D002308:Cardiolipins / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D016764:Cell Polarity / Q000187:drug effects; D003432:Cross-Linking Reagents / Q000494:pharmacology; D019281:Dimerization; D004926:Escherichia coli / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism*; D005033:Ethylmaleimide / Q000031:analogs & derivatives / Q000494:pharmacology; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009994:Osmolar Concentration; D009997:Osmotic Pressure / Q000187:drug effects; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000187:drug effects; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D027981:Symporters / Q000737:chemistry / Q000378:metabolism*
chemical_list: D002308:Cardiolipins; D003432:Cross-Linking Reagents; D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; C079244:ProP protein, E coli; D027981:Symporters; C021017:dithiobis(N-ethylmaleimide); D005033:Ethylmaleimide