Week In Science

You'll need to know something about actin to fully appreciate the propulsion patterns described by a paper entitled 'A kinematic description of the trajectories of Listeria monocytogenes propelled by actin comet tails,' authored by V. B. Shenoy, D. T. Tambe, A. Prasad, and J. A. Theriot and published in PNAS. This site provides tests and information about actin useful to both novices and those possessing familiarity with actin structures. Listeria monocytogenes, a bacterial pathogen, was the object of study. Specifically analyzed were movement patterns made as Listeria propels itself inside infected cells. The bacteria employs a unique strategy to move and evade immunological responses. It involves utilizing the cytoskeleton protein actin of a host cell. This leaves a trail of actin molecules that traces a variety of geometric shapes marking the movement of the organism. These shapes were analyzed and categorized in the paper and used to create a mechanistic model.

The capacity to trace geometrically known trails becomes compromised by mutations which skew the paths traced by Listeria and render them more vulnerable to host immune defenses. This suggests that the movement mechanism is optimized in normally functioning Listeria. As indicated by the authors, "a large variety of trajectories with a rich mathematical structure are obtained by varying the rate at which the propulsive force moves about the long axis." Among the shapes observed were circles, figure eights and sine curves.