title: A high-conductance mode of a poly-3-hydroxybutyrate/calcium/polyphosphate channel isolated from competent Escherichia coli cells.
abstract: Reconstitution into planar lipid bilayers of a poly-3-hydroxybutyrate/calcium/polyphosphate (PHB/Ca(2+)/polyP) complex from Escherichia coli membranes yields cationic-selective, 100 pS channels (Das, S., Lengweiler, U.D., Seebach, D. and Reusch, R.N. (1997) Proof for a non-proteinaceous calcium-selective channel in Escherichia coli by total synthesis from (R)-3-hydroxybutanoic acid and inorganic polyphosphate. Proc. Natl. Acad. Sci. USA 94, 9075-9079). Here, we report that this complex can also form larger, weakly selective pores, with a maximal conductance ranging from 250pS to 1nS in different experiments (symmetric 150mM KCl). Single channels were inhibited by lanthanum (IC(50)=42+/-4microM, means+/-S.E.M.) with an unusually high Hill coefficient (8.4+/-1.2). Transition to low-conductance states (<250pS) was favored by increased membrane polarization (/V/ >or=50mV). High conductance states (>250pS) may reflect conformations important for genetic transformability, or "competence", of the bacterial cells, which requires the presence of the PHB/Ca(2+)/polyP complex in the membrane.
authors.affiliation: Hotchkiss Brain Institute, Department of Physiology and Biophysics, Faculty of Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, Alta., Canada T2N 4N1. epavlov@ucalgary.ca
authors.forename: Evgeny
authors.initials: E
authors.lastname: Pavlov
authors.forename: Chelsey
authors.initials: C
authors.lastname: Grimbly
authors.forename: Catherine T M
authors.initials: CT
authors.lastname: Diao
authors.forename: Robert J
authors.initials: RJ
authors.lastname: French
mesh_terms: D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D006885:Hydroxybutyrates / Q000378:metabolism*; D015640:Ion Channel Gating; D007811:Lanthanum / Q000378:metabolism; D008051:Lipid Bilayers; D008564:Membrane Potentials; D046912:Multiprotein Complexes; D018408:Patch-Clamp Techniques; D011091:Polyesters / Q000378:metabolism*; D011122:Polyphosphates / Q000737:chemistry / Q000378:metabolism*; D000094122:Polyhydroxybutyrates
chemical_list: D002118:Calcium; D015220:Calcium Channels; D029968:Escherichia coli Proteins; D006885:Hydroxybutyrates; D007811:Lanthanum; D008051:Lipid Bilayers; D046912:Multiprotein Complexes; D011091:Polyesters; D011122:Polyphosphates; C003182:poly-beta-hydroxybutyrate; D000094122:Polyhydroxybutyrates