Thrust 2 - Interparticle Dynamics and Dynamic Cooperativity
The goal of Thrust 2 is to probe interfaces using dynamic rearrangements of colloidal particles. Tethered vesicles and their arrays. One of the core goals of IRG-2 is to create systems based on supported lipid bilayers that can be used to study integral membrane proteins and multivalent interactions among membrane-associated components. Boxer has exploited patterning methods developed earlier during CPIMA II and encoding methods based on DNA recognition to spatially array vesicles. Individual vesicles can be readily visualized by fluorescence microscopy. Their motion is being studied as a function of surface pressure, vesicle size, and charge at the air-water interface in collaboration with Fuller. These experiments are being carried out at the surfaces of water droplets with controllable surface area and the use of micron-scale bubbles provided by Longo has begun. Frank is following a complementary approach to tethered vesicles in which the vesicles are linked to a supported bilayer through a biotin-streptavidin-biotin coupling. The focus of the work is on the kinetics of the supramolecular assembly formation using the quartz crystal microbalance with dissipation. Of particular interest are shape changes in the tethered vesicles as a function of surface tethering density.
Simulation of vesicle fusion. The Pande lab has recently developed a novel technology for simulating large membrane systems and applied it to membrane fusion. Using a chemical crosslinker to restrain two fusogenic vesicles, we are able to observe fusion and computationally predict intermediates and kinetics in a quantitative and robust manner. Large-scale distributed computing (via the Folding@ Home distributed computing project) is used to build a Markovian Model of fusion kinetics by sampling a series of states and the transition probabilities between these states with coarse grained Molecular Dynamics simulation. This method builds upon the work of the Pande and Swope labs by applying methods originally designed for long timescale polymer dynamics (especially the folding of proteins and non-biological foldamers) to lipid membrane dynamics. Extensions of this model planned in the coming year include states corresponding to the encounter complex of a pair of vesicles to quantitatively predict the pair collision and interaction dynamics seen in recent Boxer lab experiments.
Colloid-based platform for studying interfacial interactions. Groves has recently developed several colloid-based bio-analytical assays using micron-sized silica particles coated with model membranes. These particles settle gravitationally into a two-dimensional dispersion where they diffuse and interact with one another eventually self-assembling into ordered or disordered structures. The colloidal structure serves as a cooperative amplifier revealing molecular events on the membrane surface without the need for labeling or complicated experimental protocols.
