Question

Results from multiple experiments suggest that the ActA protein of Listeria, an integral membrane protein expressed on the cell surface, is the only bacterial protein that is required for the movement of the bacterium within its host cell. Which combination of the following observations shows that ActA is both, necessary and sufficient for bacterial movement?

I. ActA binds to the Arp2/3 complex
II. E. Coli in which ActA is expressed moves in host cell cytosol
III. Listeria lacking the ActA gene fail to move inside the host cell cytosol.
IV. ActA has 3 transmembrane domains
V. Arp2/3, when activated, nucleates a branched actin network

a. I and II
b. II and III
c. I and III
d. III and IV
e. I and V

Answer 1

b. II and III

Explanation:

The Actin assembly-inducing (ActA) protein is an integral membrane protein localized on the bacterial surface. It has been shown that ActA is necessary and sufficient to induce bacterial movement within host cells, regardless of other proteins. The function of the ActA protein for bacterial movement within host cells was discovered by identifying mutant Listeria bacteria for the gene encoding this protein which were unable to spread from cell to cell. Subsequently, by inducing mutations in other genes of the bacterial genome, researchers discovered that actA was the only protein involved in the actin assembly, which is required for cell-to-cell spread.