Condensed Matter Seminar: "Geometry, frustration and force production in bacterial biopolymers"
Filamentous biopolymers in bacteria are involved in a variety of critical processes including templating cell growth, segregating genetic material and force production during motility and cell division. In this talk, I will discuss how a few of these systems translate biopolymer structure at multiple scales into physical function. At the molecular scale, the filamentous bacterial protein FtsZ converts chemical energy into mechanical constriction during cell division, but without the aid of any motor proteins. We show how changes in molecular level interactions leads to curvature in FtsZ and to forces at the cellular scale. At larger scales, we show that the frustrated interplay between the helicity of protein filaments, their elasticity and their interactions with the curved bacterial surface that can lead to novel conformational states with functional implications. We show that biopolymers are inherently very sensitive to this coupling and that this could be exploited for regulation of a variety of processes such as the targeted exertion of forces, signaling, and self-assembly in response to geometric cues including the local mean and Gaussian curvatures. Finally, we consider the completely disordered bacterial protein, ActA, which navigates tens of nanometers through the Gram-positive cell wall to interact with host cytoplasmic factors in the absence of any dedicated extrusion machinery. We show that the translocation process can be driven by a purely physical entropic mechanism and hence depends only on cell geometry and protein length and not on the particulars of the protein sequence.