Force spectroscopy and dynamics in biological systems

Abstract

Communication is key to any process involving the transmission of information or some sort of signal. For communication to occur, a signal must be created that can be detected. Cells communicate through cues transmitted in the forms of chemical and mechanical signals. The most fundamental means for transmitting chemical cues is through the process of diffusion. A single particle undergoing diffusion is considered to undergo Brownian motion, which can be modelled as a random walk. The random walk behavior is characteristic of both the particles properties and the fields in which it is occurring. An unbiased walk will be completely random without outside influence. A biased walk will be random within the confines of a potential influencing its direction. Both are Stochastic processes characterized through probabilistic models with known solutions. The work herein presents the development of single molecule experiments and the associated particle tracking tools targeting particles undergoing biased random walks within a trapping potential on or near a cellular membrane. In the first set of experiments, the trapping potential, an optical tweezers setup, has been developed and employed in measuring cellular membrane biophysical properties as well as blebbing forces. The optical trap was also used to directly measure flow driven forces in live embryonic zebrafish, the first known measurements of this kind. In the second set of experiments, synthetic lipid bilayers provided a trapping potential in a single dimension for protein binding experiments leading to exchanges between free, 3-dimensional diffusion and bound, or biased, 2-dimensional diffusion. In all cases, stochastic models have been used in conjunction with image-based particle tracking tools to better characterize the biophysical properties and forces associated with the cellular membrane and its means of signal transduction. These measurements are key to understanding both the chemical and mechanical signaling means by which the cellular membrane transduces an external signal into an internal response.