| Cells have no architect or organizer overseeing cellular construction or function. All cellular behaviors are instead the result of a processes termed collective molecular behavior. This means that many independent components with specific properties and abilities act together through random encounters to produce all of the traits of the cell. One exquisite example of this is the actin cytoskeleton, which gives the cell shape, allows motility and adhesion, and is critical in many other processes such as endocytosis and molecular transport. Some components of the actin cytoskeleton are well studied and organizing principles are beginning to be understood. Unfortunately many mysteries remain and many models of behaviors must therefore make assumptions about how components function and interact. The work presented here directly tests some basic assumption and works to improve the fidelity of our models of collective molecular behavior.;Actin crosslinking proteins perform a simple role in cells, linking together two or more actin filaments into higher order structures. It has been known for some time that different crosslinkers have a propensity to form and localize to different structures, however the molecular basis for this is not known. Data presented here directly shows that some crosslinking proteins have preferences for interaction with specific actin structures. Specifically, alpha-actinin is a promiscuous crosslinking protein, crosslinking all geometries of actin presented, while fascin is geometrically selective, only crosslinking filaments that are arranged in a parallel orientation. Additionally both fimbrin and espin are shown to bind aligned filaments.;Actin crosslinking proteins are also thought to be dynamic within the context of actin based structures. Experimental data presented here using fascin-actin bundles show that dynamics are dependent on a competition between free and bound crosslinking protein, while structures that exist absent challenge show little sign of dynamics.;This data places limits on the function of multiple different crosslinking proteins and models of in vitro and in vivo behavior, bringing us one step closer to understanding how the cell functions in the absence of outside direction. |
