Listeria monocytogenes phosphatidylinositol-specific phospholipase C has evolved for virulence by greatly reduced activity on GPI anchors

Listeria monocytogenes phosphatidylinositol-specific phospholipase C (PI-PLC) plays a critical role in escape of this human pathogen from host cell vacuoles. Unlike classical bacterial PI-PLCs, the L. monocytogenes enzyme has very weak activity on glycosylphosphatidylinositol (GPI)-anchored proteins. Previous crystal structure analysis has revealed that a small beta-strand (Vb) is present in Bacillus cereus PI-PLC and is absent in the enzyme from L. monocytogenes. This Vb beta-strand in B. cereus PI-PLC forms contacts with the glycan linker of GPI anchors, which presumably increases its activity on GPI-anchored proteins. In this study, we show that, of all known bacterial PI-PLCs, those from listeriae are the only ones that lack the beta-strand. Expression by L. monocytogenes of B. cereus PI-PLC, which has strong activity on GPI-anchored proteins, inhibited bacterial escape from a vacuole and cell-to-cell spread, resulting in greatly reduced virulence in mice. Deletion of the Vb beta-strand from B. cereus PI-PLC abolished its ability to cleave GPI-anchored proteins, decreased its inhibitory effects, and increased its virulence in mice. These results strongly suggest that L. monocytogenes PI-PLC has evolved as an important determinant of L. monocytogenes pathogenesis by absence of the Vb beta-strand, thus leading to greatly reduced activity on GPI-anchored proteins.