Ajay Gopinathan, Ph.D., University of California, Merced
Filamentous protein biopolymers are a fundamental biomaterial involved in a variety of critical cellular processes. In bacteria, these include 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 an intrinsic incompatibility between the geometry of the filament and that of its local environment 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 certain protein filaments and the curvature of the bacterial surface to which they bind, 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 a completely disordered bacterial protein 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 this translocation process can be driven by a purely physical entropic mechanism that depends only on the mismatch between cell geometry and protein length and not on the particulars of the protein sequence.