Control of Bacterial Virulence through the Peptide Signature of the Habitat

Abstract

Summary: To optimize fitness, pathogens selectively activate their virulence program upon host entry. Here, we report that the facultative intracellular bacterium Listeria monocytogenes exploits exogenous oligopeptides, a ubiquitous organic N source, to sense the environment and control the activity of its virulence transcriptional activator, PrfA. Using a genetic screen in adsorbent-treated (PrfA-inducing) medium, we found that PrfA is functionally regulated by the balance between activating and inhibitory nutritional peptides scavenged via the Opp transport system. Activating peptides provide essential cysteine precursor for the PrfA-inducing cofactor glutathione (GSH). Non-cysteine-containing peptides cause promiscuous PrfA inhibition. Biophysical and co-crystallization studies reveal that peptides inhibit PrfA through steric blockade of the GSH binding site, a regulation mechanism directly linking bacterial virulence and metabolism. L. monocytogenes mutant analysis in macrophages and our functional data support a model in which changes in the balance of antagonistic Opp-imported oligopeptides promote PrfA induction intracellularly and PrfA repression outside the host. : We identify a major control mechanism of Listeria virulence based on antagonistic regulation by environmental peptides. Activity levels of the virulence regulator PrfA depend on the net balance between the rates of synthesis of the PrfA-activating cofactor GSH from exogenous peptide-derived cysteine and of direct, promiscuous PrfA inhibition by non-cysteine-containing peptides. Keywords: Listeria monocytogenes, Listeria virulence regulation, PrfA allosteric regulation, environmental control of bacterial virulence, virulence regulation by nutritional peptides, Opp transport system, transcription factor regulation by peptides, PrfA-peptide 3D structure, PrfA-glutathione regulation