A high-conductance mode of a poly-3-hydroxybutyrate/calcium/polyphosphate channel isolated from competent Escherichia coli cells

Reconstitution into planar lipid bilayers of a poly-3-hydroxybutyrate/ calcium/polyphosphate (PHB/Ca²⁺/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 250 pS to 1 nS in different experiments (symmetric 150 mM KCl). Single channels were inhibited by lanthanum (IC₅₀ = 42 ± 4 μM, means ± S.E.M.) with an unusually high Hill coefficient (8.4 ± 1.2). Transition to low-conductance states (<250 pS) was favored by increased membrane polarization (|V| ≥ 50 mV). High conductance states (>250 pS) 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.