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Emerging Concepts in Ion Channel Biophysics
Friday Speaker Abstracts
32
Lipid-protein Interactions in Model Membranes
Andrea Alessandrini
.
CNR-Institute of Nanoscience, Modena, Italy.
Lipids and proteins work together to ensure that the biological membrane fulfills its functions. In
this teamwork, lipids can affect the activity of protein ion channels both by the action of specific
interactions and, indirectly, by their physical-chemical properties. Here we will concentrate on
how the lipid bilayer assembled in different model systems could affect the action of membrane
proteins by means of its peculiar thermodynamic and mechanical properties. We will show that
the presence of a phase coexistence state in a lipid bilayer is able to significantly affect the
conductance, the open probability and the dwell times of KcsA channels. We will use different
model systems (Black Lipid Membranes, Supported Lipid Bilayers) and biophysical techniques
(Differential Scanning Calorimetry, Atomic Force Microscopy) to present a consistent
interpretation of the single channel data obtained by the voltage-clamp technique. In particular,
we will illustrate, by Atomic Force Microscopy imaging and Spectroscopy, that KcsA channels
prefer to partition into the liquid disordered phase and that this phase is characterized by a
mechanical softening behavior in the transition region. We will also show other examples in
which it emerges that the physical properties of lipid bilayers should be included in the analysis
of the effects of exogenous molecules on ion channels. These examples include the action of
neurosteroids and antimicrobial peptides on model lipid bilayers. Neurosteroids are modulators
of ligand gated ion channels whose mode of action probably involves a strong interaction with
the lipid bilayer, whereas antimicrobial peptides are relevant host-defense peptides strongly
interacting with the membrane of bacteria and fungi. In both cases we will use different model
systems such as GUVs and SLBs.