Binding of avidin modified antibody to biotinylated metal supported membranes and liposomes changes the physical properties of lipid bilayer.

Various methods have been applied to study the physical properties of metal supported bilayer lipid membranes (s-BLM) and large unilamellar liposomes containing biotinylated phospholipids during the binding of IgG modified by avidin. Electrostriction method applied to s-BLM showed that addition of avidin-IgG (A-IgG) complex in a small concentration (0.2 mumol/l) resulted in an approximately twofold decrease of membrane capacitance, C, increase of elasticity modulus in direction perpendicular to the membrane plane, E perpendicular, by 5-20%, increase in intrinsic membrane potential, delta phi m, by approximately 30 mV, and an approximately 5-15% increase of the coefficient of dynamic viscosity, eta. The method of ultrasonic velocimetry showed that addition into the suspension of liposomes of unmodified IgG did not induce any changes in ultrasound velocity, while addition of A-IgG complex in a concentration range of 0-1 mumol/l led to an increase of the velocity number [u]. The plot of changes of [u] versus A-IgG concentration has a tendency to saturate at concentrations above 0.5 mumol/l, which suggests long-range interactions in the membrane induced by strong binding of A-IgG to the biotin sites on the membrane. Probably, this binding leads to a decrease of the coefficient of adiabatic compressibility of liposomes.