A PEST-like sequence in listeriolysin O essential for Listeria monocytogenes pathogenicity.

Establishment and maintenance of an intracellular niche are critical to the success of an intracellular pathogen. Here, the pore-forming protein listeriolysin O (LLO), secreted by Listeria monocytogenes, was shown to contain a PEST-like sequence (P, Pro; E, Glu; S, Ser; T, Thr) that is essential for the virulence and intracellular compartmentalization of this pathogen. Mutants lacking the PEST-like sequence entered the host cytosol but subsequently permeabilized and killed the host cell. LLO lacking the PEST-like sequence accumulated in the host-cell cytosol, suggesting that this sequence targets LLO for degradation. Transfer of the sequence to perfringolysin O transformed this toxic cytolysin into a nontoxic derivative that facilitated intracellular growth.