Parvulin-type PPIase, PrsA, contributes to folding and stability of virulence factors that determine pathogenicity in Gram-positive bacteria

During host infection, post-translocational molecular chaperones in Gram-positive bacteria function to regulate secreted virulence factors. These virulent proteins are secreted in an unfolded state and in order contribute to pathogenesis, they must be properly folded. One chaperone, named PrsA, is present in many pathogenic Gram-positive bacteria and contributes to the ability of those bacteria to infect their hosts. The mechanisms in which PrsA proteins stabilize and facilitate the full functionality of their client proteins are largely understudied. Therefore, I used Gram-positive bacteria Listeria monocytogenes (Lm) and Streptococcus pneumoniae (Sp) as model bacterial organisms to uncover these molecular mechanisms. During host cell infection, L. monocytogenes and S. pneumoniae secrete virulence factors across the bacterial membrane, to an area between the membrane and cell well. This interface is solvent accessible and may expose secreted proteins to a harsh environment problematic for protein folding. PrsA proteins, which function as post-translocational molecular chaperones and PPIases, are present in the cell wall-membrane interface of Gram-positive bacteria and I hypothesize PrsA is responsible for the full functionality and stability of secreted virulence proteins. Here, I present my findings of the relationship between the pore-forming toxins listeriolysin-O (LLO) and pneumolysin (Ply) with LmPrsA2 and SpPrsA, respectively. Our data shows that LmPrsA2 and SpPrsA interact with many virulence factors, and despite the loss of the entire PPIase domain, they can retain strong interactions with LLO and Ply, which are thought to be folded by the PPIase and/or foldase domains. Our data highlight the potential for an antimicrobial candidate capable of decreasing the spread and growth of Lm and Sp by inhibiting the hydrophobic binding pocket of the PrsA foldase domain