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Biophys J, October 1999, p. 2066-2074, Vol. 77, No. 4
*Universität Würzburg, Physikalisches Institut EP-5, 97074 Würzburg, Germany and #Center for Ultrastructure Research and Ludwig-Boltzmann-Institute for Molecular Nanotechnology, Universität für Bodenkultur Wien, A-1180 Vienna, Austria
A dedicated dynamic light scattering (DLS) setup was
employed to study the undulations of freely suspended planar lipid
bilayers, the so-called black lipid membranes (BLM), over a previously
inaccessible spread of frequencies (relaxation times ranging from
10
2 to 10
6 s) and wavevectors (250 cm
1 < q < 38,000 cm
1). For a BLM consisting of
1,2-dielaidoyl-sn-3-glycero-phosphocholine (DEPC) doped
with two different proportions of the cationic lipid analog
dioctadecyl-dimethylammonium bromide (DODAB) we observed an increase of
the lateral tension of the membrane with the DODAB concentration. The
experimentally determined dispersion behavior of the transverse shear
mode was in excellent agreement with the theoretical predictions of a
first-order hydrodynamic theory. The symmetric adsorption of the
crystalline bacterial cell surface layer (S-layer) proteins from
Bacillus coagulans E38-66 to a weakly cationic BLM (1.5 mol % DODAB) causes a drastic reduction of the membrane tension well
beyond the previous DODAB-induced tension increase. The likely reason
for this behavior is an increase of molecular order along the lipid
chains by the protein and/or partial protein penetration into the lipid
headgroup region. S-layer protein adsorption to a highly cationic BLM
(14 mol % DODAB) shows after 7 h incubation time an even stronger
decrease of the membrane tension by a factor of five, but additionally
a significant increase of the (previously negligible) surface
viscosity, again in excellent agreement with the hydrodynamic theory.
Further incubation (24 h) shows a drastic increase of the membrane
bending energy by three orders of magnitude as a result of a
large-scale, two-dimensional recrystallization of the S-layer proteins
at both sides of the BLM. The results demonstrate the potential of the
method for the assessment of the different stages of protein adsorption
and recrystallization at a membrane surface by measurements of the
collective membrane modes and their analysis in terms of a hydrodynamic theory.
Biophys J, October 1999, p. 2066-2074, Vol. 77, No. 4
© 1999 by the Biophysical Society 0006-3495/99/10/2066/09 $2.00
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