The Intracellular Cyclophilin PpiB Contributes to the Virulence of Staphylococcus aureus Independently of Its Peptidyl-Prolyl <i>cis/trans</i> Isomerase Activity

Abstract

The <i>Staphylococcus aureus</i> cyclophilin PpiB is an intracellular peptidyl prolyl <i>cis/trans</i> isomerase (PPIase) that has previously been shown to contribute to secreted nuclease and hemolytic activity. In this study, we investigated the contribution of PpiB to <i>S. aureus</i> virulence. Using a murine abscess model of infection, we demonstrated that a <i>ppiB</i> mutant is attenuated for virulence. We went on to investigate the mechanism through which PpiB protein contributes to virulence, in particular the contribution of PpiB PPIase activity. We determined the amino acid residues that are important for PpiB PPIase activity and showed that a single amino acid substitution (F64A) completely abrogates PPIase activity. Using purified PpiB F64A protein <i>in vitro</i>, we showed that PPIase activity only partially contributes to Nuc refolding and that PpiB also possesses PPIase-independent activity. Using allelic exchange, we introduced the F64A substitution onto the <i>S. aureus</i> chromosome, generating a strain that produces enzymatically inactive PpiB. Analysis of the PpiB F64A strain revealed that PPIase activity is not required for hemolysis of human blood or virulence in a mouse. Together, these results demonstrate that PpiB contributes to <i>S. aureus</i> virulence via a mechanism unrelated to prolyl isomerase activity.