The protein machinery controlling membrane fusion (or fission) has been well studied; however, the role of vesicle diffusion near membranes in these critical processes remains unclear. We experimentally and theoretically investigated the dynamics of small vesicles (∼50 nm in diameter) that are diffusing near supported planar bilayers acting as "target" membranes. Using total internal reflection-fluorescence correlation spectroscopy, we examined the validity of theoretical analyses of vesicle-membrane interactions. Vesicles were hindered by hydrodynamic drag as a function of their proximity to the planar bilayer. The population distributions and diffusion kinetics of the vesicles were further affected by changing the ionic strength and pH of the buffer, as well as the lipid composition of the planar membrane. Effective surface charges on neutral bilayers were also analyzed by comparing experimental and theoretical data, and we show the possibility that vesicle dynamics can be modified by surface charge redistribution of the planar bilayer. Based on these results, we hypothesize that the dynamics of small vesicles, diffusing close to biomembranes, may be spatially restricted by altering local physiological conditions (e.g., salt concentration, lipid composition, and pH), which may represent an additional mechanism for controlling fusion (or fission) dynamics.
Bibliographical noteFunding Information:
This work is supported, in part, by The Pennsylvania State University, the Penn State Materials Research Institute, the Penn State Materials Research Science and Engineering Center (under National Science Foundation grant DMR 0213623), and the Lehigh-Penn State Center for Optical Technologies, which is supported by the Commonwealth of Pennsylvania. Acknowledgment is also made to the Donors of the American Chemical Society Petroleum Research Fund, National Institutes of Health grant AG030949, National Science Foundation grant MCB 0718741, and Avanti Polar Lipids for partial support of this research.