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

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Abstract
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) may reflect conformations important for genetic transformability, or “competence”, of the bacterial cells, which requires the presence of the PHB/Ca2+/polyP complex in the membrane.

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