Differential effects of temperature on E-coli and synthetic polyhydroxybutyrate/polyphosphate channels

Complexes of poly-(R)-3-hydroxybutyrate and inorganic polyphosphate (PHB/polyP), isolated from the plasma membranes of Escherichia coli or prepared synthetically (HB128/polyP(65)), form Ca2+- selective ion channels in planar lipid bilayers that exhibit indistinguishable gating and conductance characteristics at 22 degreesC. Here we examine the gating and conductance of E. coli and synthetic PHB/polyP complexes in planar lipid bilayers as a function of temperature from 15 to 45 degreesC. E. coli PHB/polyP channels remained effectively open throughout this range, with brief closures that became more rare at higher temperatures. Conversely, as temperatures were gradually increased, the open probability of HB128/polyP(65) channels progressively decreased. The effect was fully reversible. Channel conductance exhibited three distinct phases. Below 25 degreesC, as PHB approached its glass temperature (ca. 10 degreesC), the conductance of both E. coli and synthetic channels remained at about the same level (95-105 PS). Between 25 degreesC and ca. 40 degreesC, the conductance of E. coli and synthetic channels increased gradually with temperature coefficients (Q(10)) of 1.45 and 1.42, respectively. Above 40 degreesC, E. coli channel conductance increased sharply, whereas the conductance of HB128/polyP(65) channels leveled off. The discontinuities in the temperature curves for E. coli channels coincide with discontinuities in thermotropic fluorescence spectra and specific growth rates of E. coli cells. It is postulated that E. coli PHB/polyP complexes are associated with membrane components that inhibit their closure at elevated temperatures.