9:00–10:00 am
Please join us:
Danielle R. Scheff’s PhD Thesis Defense
Tuesday, July 13, 2021, 9:00 AM CDT
INTERPLAY OF STRUCTURE, MECHANICS, AND DYNAMICS IN BIOPOLYMER NETWORKS
Cells dynamically control their material properties through remodeling of the actin cytoskeleton, an assembly of cross-linked networks and bundles formed from the filamentous biopolymer actin. Actin thus serves as an ideal model system to study the underlying mechanisms of mechanical adaptation in cells. In this talk, I reconstitute networks of purified proteins to investigate the interplay of three aspects of actin: structure, mechanics, and dynamics.
First, I explore how actin networks adapt to external stimuli through structural changes. It was recently found that cross-linked networks of actin filaments can exhibit adaptive behavior where an applied shear stress can induce asymmetry in the nonlinear elasticity. By varying cross-linker concentration and physical properties in both experimental and simulated systems, I probe the origin of this effect and find that it depends on two conditions: the initial network must exhibit nonlinear strain stiffening, and filaments in the network must be able to reorient during training. Then, I investigate the ability of cross-linkers and the molecular motor myosin to control turnover, a dynamic process in which actin continuously polymerizes on one end while depolymerizing on the other. I find that using cross-linkers to bundle actin prevents severing by actin binding protein cofilin, which similarly prevents turnover. However, I also find that myosin buckling is able to increase turnover even in bundled network. These results suggest that not only can myosin regulate turnover of actin filaments, but also that different methods of disassembly might be needed to remodel actin depending on its local structure.
Committee members:
Margaret Gardel (Chair)
Heinrich Jaeger
Young-Kee Kim
Arvind Murugan