Julie Theriot
Assistant Professor
Departments of Biochemistry and of Microbiology & Immunology
Stanford University School of Medicine
 

The shape of eukaryotic cells is primarily determined by the organization of filamentous protein polymers, collectively called the "cytoskeleton". Actin is the most abundant of the cytoskeletal proteins, a small globular protein that can self-associate to form helical filaments thousands of subunits in length.  Polymerizing networks of actin filaments are capable of exerting significant mechanical forces, used by many eukaryotic cells to change shape or to move.  Certain intracellular bacterial pathogens have developed the ability to induce the polymerization of host cell actin filaments on their surface and to harness the resulting force for efficient intra- and intercellular spread.  Bacteria infecting a human cell are initially covered with a uniform "cloud" of actin filaments, which then breaks symmetry and forms a highly polarized "comet tail" structure as the bacteria start to move.  We have found that latex microspheres coated with a single bacterial protein are able to form actin clouds and comet tails and move in a manner indistinguishable from living bacteria.  I will describe our current work towards understanding the biophysical basis of force generation and symmetry-breaking in this biological system.