In the optical trap experiment, laser light is used to hold the bead and the bundle next to the nanofabricated wall. Is work being done against the laser light focused at the bead and/or the light focused along the bundle?
What is the Reynolds number and why is it relevant when studying Listeria motility?How would you expect the rate of actin growth to change when pulling up or pushing down on the back of the cantilever?
What might account for the load-independent behavior of ActA growth, as demonstrated using AFM?
Lasa et al. describe a Listeria ActA mutant that exhibits a hopping behavior (Lasa et al. (1997). EMBO. 16: 1531-40). The mutant Listeria moves in a discontinuous manner, where periodic spots of dense actin (~2microns in length which is about the size of the bacterium) are spaced by distances of 1 to 4 microns. The speed of the bacterium occurs in bursts that coincide with the bursts of actin polymerization. The average speed of the wild-type Listeria is twice as fast as the mutant, but the burst speed of the mutant, which peaks as the bacterium emerges from the actin sheath, is around four times faster than wild-type Listeria.
Suggest a role for ActA in addition to Arp2/3 complex mediated actin polymerization. Extend the watermelon seed analogy used in lecture. Compare wild-type Listeria with the ActA mutant. If the watermelon seed is Listeria and your fingers are a comet tail, what would the outcome be when squeezing your fingers when using wild-type Listeria, what would you expect when using the mutant?