After gaining entry into the host cell by the zipper mechanism, the bacterium Listeria monocytogenes escapes phagosomes by secreting listeriolysin O. This protein …
A) is active at neutral pH and cannot be degraded by the proteasome.
B) is active at neutral pH and is rapidly degraded by the proteasome.
C) is active at acidic pH and cannot be degraded by the proteasome.
D) is active at acidic pH and is rapidly degraded by the proteasome.
E) is active at basic pH and cannot be degraded by the proteasome.

Question

After gaining entry into the host cell by the zipper mechanism, the bacterium Listeria monocytogenes escapes phagosomes by secreting listeriolysin O. This protein …
A)	is active at neutral pH and cannot be degraded by the proteasome.
B)	is active at neutral pH and is rapidly degraded by the proteasome.
C)	is active at acidic pH and cannot be degraded by the proteasome.
D)	is active at acidic pH and is rapidly degraded by the proteasome.
E)	is active at basic pH and cannot be degraded by the proteasome.

Quizplus · Accepted Answer

Listeriolysin O disrupts the phagosomal membrane and releases the bacterium into the host-cell cytosol. Despite its persisting secretion, this protein does not disrupt other cellular membranes since it is much less active at the neutral pH of the cytosol, and also because it is rapidly degraded by the host proteasomes.

After Gaining Entry into the Host Cell by the Zipper