Isolated protein subunits of the crystalline bacterial cell surface layer (S-layer) of Bacillus coagulans E38-66 have been recrystallized on one side of planar black lipid membranes (BLMs) and their influence on the electrical properties, rupture kinetics and mechanical stability of the BLM was investigated. The effect on the boundary potential, the capacitance or the conductance of the membrane was negligible whereas the mechanical properties were considerably changed. The mechanical stability was characterized by applying voltage pulses or ramps to induce irreversible rupture. The amplitude of the voltage pulse leading to rupture allows conclusions on the ability of membranes to resist external forces. Surprisingly, these amplitudes were significantly lower for composite S-layer/lipid membranes compared to undecorated BLMs. In contrast, the delay time between the voltage pulse and the appearance of the initial defect was found to be drastically longer for the S-layer-supported lipid bilayer. Furthermore, the kinetics of the rupture process was recorded. Undecorated membranes show a fast linear increase of the pore conductance in time, indicating an inertia-limited defect growth. The attachment of an S-layer causes a slow exponential increase in the conductance during rupture, indicating a viscosity-determined widening of the pore. In addition, the mechanical properties on a longer time scale were investigated by applying a hydrostatic pressure across the BLMs. This causes the BLM to bulge, as monitored by an increase in capacitance. Compared to undecorated BLMs, a significantly higher pressure gradient has to be applied on the S-layer face of the composite BLMs to observe any change in capacitance.

We investigate the stability and rupture kinetics of planar lipid membranes covered with electrostatically adsorbed polyelectrolytes. After black lipid membranes were formed from negatively charged lipids, polylysines (PLs) of different molecular weights (MW) were added on one or on both sides of the membrane. The adsorption of PL was detected by recording changes of the transmembrane voltage. Rupture was induced by applying short voltage pulses across the membrane. The voltage causing breakdown of the membrane gives information on its mechanical stability. Adsorption of PL on one side of the membrane leads to an asymmetric transmembrane potential, which adds to the externally applied voltage. High MW PL decreases the critical breakdown voltage of the membrane significantly but also increases the delay time between the voltage pulse and pore formation. It is further shown that PL alters the time course of pore widening in a molecular weight-dependent manner. Low MW PL-decorated membranes and undecorated membranes show a fast rupture determined by inertia. In contrast, adsorption of high MW PLs causes a dramatic decrease of the rupture velocity. In this case, the rupture velocity is determined by viscosity. An analysis of the rupture kinetics allows an estimate of the 2D viscosity.

We investigate the influence of surface charges on the rupture of black lipid membranes ͑BLM͒. Rupture is induced by short electric voltage pulses across the membrane. The average voltage necessary to induce breakdown gives information on the energy barrier of defect formation. The rapid transmembrane voltage decay during rupture allows one to evaluate the kinetics of defect widening. The breakdown voltage is about the same for BLM made of lipids with phosphatidylserine headgroups and for BLM made of lipids with phosphatidylcholine headgroups. Moreover, the breakdown voltage is independent of the ionic strength of the aqueous medium surrounding the BLM. This indicates that the stability of the BLM is not dominated by mutual electrostatic repulsion of the headgroups. However, the breakdown voltage depends on the type of the hydrophobic chains of the lipids. Palmitoyl-oleoyl ͑PO͒ membranes require ϳ100-mV smaller breakdown voltages compared to diphytanoyl ͑DPh͒ membranes. Surprisingly, the rupture kinetics depends on the hydrocarbon chains. It was found to be four times faster for DPh than for PO membranes, and independent of the type of headgroup.

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We have investigated the binding of the effector domains of myristoylated alanine-rich C kinase substrate (MARCKS) and of MARCKS-related protein (MRP) to lipid model membranes. For membrane systems we used lipid monolayers on a Langmuir trough and black lipid membranes (BLM). The binding of the peptides was detected by monitoring changes in the boundary potential of the lipid membranes. The vibrating plate technique (VPT) and the method of inner field compensation (IFC) were used for the monolayer and for the BLM, respectively. We could show that the effector domain of MARCKS binds to acidic lipid membranes mainly via electrostatic interactions and to zwitterionic lipid membranes via hydrophobic interactions. Isobaric measurements on lipid monolayers revealed that binding of both effector domains is accompanied by partial insertion of the peptides into the membrane. Adsorption and insertion of the peptides could be followed simultaneously by the VPT and by recording the increase in area of the lipid monolayer, respectively. No temporal delay could be observed between adsorption and insertion of the peptides, demonstrating that adsorption is the rate-limiting step and that insertion is faster than the time resolution of the experiments, i.e., a few seconds. Both the IFC and the VPT did not show any significant difference between the behaviors of the effector domains of MARCKS and MRP. With the IFC we show that calcium can regulate the translocation of the MARCKS effector peptide between the membrane and calmodulin (CaM) in the bulk. Our results indicate, that the IFC and VPT are suitable qualitatively, and to a certain extent quantitatively, as membrane binding assays.