The ability of the phosphatidylinositol-specific phospholipase C (PI-PLC) from Listeria monocytogenes to hydrolyze glycosyl phosphatidylinositol (GPI)-anchored membrane proteins was compared with the ability of the PI-PLC from Bacillus thuringiensis to hydrolyze such proteins. The L. monocytogenes enzyme produced no detectable release of acetylcholinesterase from bovine, sheep, and human erythrocytes. The cleavage of the GPI anchors of alkaline phosphatase from rat and rabbit kidney slices was less than 10% of the cleavage seen with the PI-PLC from B. thuringiensis. Activity for release of Fcy receptor IIIB (CD16) on human granulocytes was also low. Variations in pH and salt concentration had little effect on the release of GPI-anchored proteins. Our data show that L. monocytogenes PI-PLC has low activity on GPI-anchored proteins.Phosphatidylinositol-specific phospholipase C (PI-PLC) is secreted by Several species of gram-positive bacteria, including the human pathogens Staphylococcus aureus (16), Clostridium novyi (26), and Bacillus anthracis (14). However, a role for this enzyme in the pathogenesis of the diseases caused by these organisms has not been defined. Recently, PI-PLC was identified as one of several proteins secreted by Listeria monocytogenes, a facultatively intracellular human and animal pathogen (3,12,19). The protein has been overexpressed in L. monocytogenes, purified to homogeneity, and characterized with respect to substrate specificity and in vitro requirements for enzyme activity (7). Like other prokaryotic PI-PLCs, the L. monocytogenes enzyme was found to be specific for phosphatidylinositol (PI) and to have no detectable activity on phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate, which are involved in signal transduction in mammalian cells (1).Bacterial PI-PLCs were originally discovered as a result of their ability to cleave glycosyl-phosphatidylinositol (GPI)-anchored membrane proteins at the PI terminus (14, 15), and all bacterial PI-PLCs appear to possess this activity. When the purified enzyme from L. monocytogenes was tested on the membrane form of the variant surface glycoprotein of Trypanosoma brucei, it was able to cleave the GPI anchor; however, its activity was approximately 10% of the activity of the PI-PLC from Bacillus thuringiensis when equivalent PI hydrolysis units were compared (7). Since GPI-anchored proteins are potential targets for this facultatively intracellular pathogen during its entry into host cells by phagocytosis (3, 19) and subsequent escape from phagocytic vacuoles (4), we further explored the ability of L. monocytogenes PI-PLC (PT-PLCL.m.) to release these proteins from cell membranes. Our data show that this enzyme has little or no activity for * Corresponding author.
GPI-anchored proteins obtained from a variety of human and animal tissues.Release of acetylcholinesterase from erythrocytes. Erythrocytes (bovine and sheep cells obtained from Rockland, Inc., Gilbertsville, Pa.; human erythrocytes obtained from peripheral blood of...