Changes in single K⁺ channel behavior induced by a lipid phase transition

Abstract

Membrane proteins activity is affected by the properties of the lipid bilayer hosting them. These properties are established by both the lipid composition and the thermodynamic state of the bilayer. In the latter case, any parameter which can alter the state of the bilayer is indirectly able to affect the activity of membrane proteins. In a recent study, we have demonstrated that the activity of the KcsA ion channel is strongly related to the thermodynamic state of the lipid bilayer. In particular, when the lipid bilayer is in its main phase transition region, the conductivity of KcsA is increased and all its characteristic times change according to the characteristic times of the lipid bilayer. We propose here that the lipid bilayer can affect the distribution among many conformational substates of the open channel, affecting the corresponding channel conductivity. 

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Figures and Tables

Figure 1 (A) Scheme of a KcsA molecule in the lipid bilayer at the phase transition region. The channel is confined in the liquid disordered (l_d) domains and mainly excluded from the solid ordered (s_o) ones.14 (B) By decreasing the temperature the single channel conductance initially decreases and, in the case of a POPE:POPG 3:1 bilayer, at a temperature of about 22°C a trend inversion is observed. The trend inversion occurs at the temperature when the phase transition of the bilayer is supposed to start. For a POPG bilayer, for which no phase transition is expected in the observed temperature range, a monotonic behavior is observed for the single channel conductance.

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