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Diffusive Dynamics of Vesicles Tethered to a Fluid Supported Bilayer by Single-Particle Tracking
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posted on 2006-06-20, 00:00 authored by Chiaki Yoshina-Ishii, Yee-Hung M. Chan, Joseph M. Johnson, Li A. Kung, Peter Lenz, Steven G. BoxerWe recently introduced a method to tether intact phospholipid vesicles onto a fluid supported lipid bilayer using
DNA hybridization (Yoshina-Ishii, C.; Miller, G. P.; Kraft, M. L; Kool, E. T.; Boxer, S. G. J. Am. Chem. Soc. 2005,
127, 1356−1357). Once tethered, the vesicles can diffuse in two dimensions parallel to the supported membrane
surface. The average diffusion coefficient, D, is typically 0.2 μm2/s; this is 3−5 times smaller than for individual lipid
or DNA-lipid conjugate diffusion in supported bilayers. In this article, we investigate the origin of this difference in
the diffusive dynamics of tethered vesicles by single-particle tracking under collision-free conditions. D is insensitive
to tethered vesicle size from 30 to 200 nm, as well as a 3-fold change in the viscosity of the bulk medium. The addition
of macromolecules such as poly(ethylene glycol) reversibly stops the motion of tethered vesicles without causing the
exchange of lipids between the tethered vesicle and supported bilayer. This is explained as a depletion effect at the
interface between tethered vesicles and the supported bilayer. Ca ions lead to transient vesicle−vesicle interactions
when tethered vesicles contain negatively charged lipids, and vesicle diffusion is greatly reduced upon Ca ion addition
when negatively charged lipids are present both in the supported bilayer and tethered vesicles. Both effects are
interesting in their own right, and they also suggest that tethered vesicle-supported bilayer interactions are possible;
this may be the origin of the reduction in D for tethered vesicles. In addition, the effects of surface defects that reversibly
trap diffusing vesicles are modeled by Monte Carlo simulations. This shows that a significant reduction in D can be
observed while maintaining normal diffusion behavior on the time scale of our experiments.