The serine-rich C-terminal tail of the Listeria monocytogenes secretion chaperone PrsA2 is critical for bacterial virulence and resistance to cell-wall active antibiotics.

Protein intrinsically disordered regions (IDRs) are characterized by their lack of defined stable tertiary structure and are capable of adopting multiple conformations for functional activity. In chaperone proteins, these flexible regions are often sites of condition specific protein-protein interactions. In Listeria monocytogenes (Lm), PrsA2 is a peptidyl prolyl isomerase (PPIase) chaperone that promotes pathogenesis through the maturation of secreted proteins including the pore forming toxin, listeriolysin O (LLO). PrsA2 is composed of a PPIase domain and foldase domain that are critical for secreted protein function. In addition, PrsA2 contains an uncharacterized unstructured region, the carboxyl-terminal tail (C-tail) consisting of 10-amino acid residues rich in serine. Here, we demonstrate that the PrsA2 C-tail and its serine residues are critical for Lm bacterial virulence in a mouse septicemic model. We trace this virulence defect to a reduction in secreted LLO activity exhibited by Lm PrsA2 C-tail bacterial mutants. Further, we use biophysical and biochemical assays to establish that the PrsA2 C-tail is required for interacting with and folding the LLO toxin. We then characterize the PrsA2 C-tail as a critical factor in Lm survival under stress conditions and highlight its crucial role against cell-wall targeting antibiotics. PrsA homologs are well-conserved in Gram-positive bacteria, and this work characterizes the Lm PrsA2 C-tail, demonstrating its contribution to bacterial virulence, chaperone function, and secreted protein activity.