Observation and Kinematic Description of Long Actin Tracks Induced by Spherical Beads

Abstract

We report an in vitro study comparing the growth of long actin tails induced by spherical beads coated with the verprolin central acidic domain of the polymerization enzyme N-WASP to that induced by Listeria monocytogenes in similar cellular extracts. The tracks behind the beads show characteristic differences in shape and curvature from those left by the bacteria, which have an elongated shape and a similar polymerization-inducing enzyme distributed only on the rear surface of the cell. The experimental tracks are simulated using a generalized kinematic model, which incorporates three modes of bead rotation with respect to the tail. The results show that the trajectories of spherical beads are mechanically deterministic rather than random, as suggested by stochastic models. Assessment of the bead rotation and its mechanistic basis offers insights into the biological function of actin-based motility.

Trajectories ofListeria-type motility in two dimensions

“…Due to the addition of new actin monomers, the actin network is deformed and the resulting stress pushes the load. Since many experimental observations of actin-based motility were performed in a quasi-two-dimensional space [17,18], for the purpose of understanding the fundamental physical mechanisms for generating curved trajectories, we consider a disk moving in two dimensions.…”

“…We express θ N 1 v c and θ F 1 v c as linear combinations of θ N 1 F 1 , θ N 1 N 2 , and θ N 1 F 2 by solving Eqs. (17) and (18), then straightforward algebra leads to the linearized equations for the angles,…”

“…Besides the aforementioned experimental, theoretical, and computational works, recently there is a growing interest in the dynamics of actin-based motility on a much longer time scale, as such studies could probe the dynamics of actin network reorganization during the motion of a load [17][18][19]. In particular, in experiments on Listeria and functionalized beads in cell extracts, various geometrical trajectories including circles, S-shaped curves, and translating figure eights [17,18] have been observed.…”

“…In particular, in experiments on Listeria and functionalized beads in cell extracts, various geometrical trajectories including circles, S-shaped curves, and translating figure eights [17,18] have been observed. It is unlikely that these geometrical trajectories could be a result of the random fluctuations of the force generated on the load [20].…”

“…It is unlikely that these geometrical trajectories could be a result of the random fluctuations of the force generated on the load [20]. Kinematic descriptions [17,18,21] suggested that rotation of the propulsive force around the load can generate these geometrical trajectories. It has also been shown in a microscopic model that these trajectories can be reproduced by assuming an asymmetric actin force distribution on the load [22].…”