PURIFICATION AND CHARACTERIZATION OF AN EXTRACELLULAR 29-KILODALTON PHOSPHOLIPASE-C FROM LISTERIA-MONOCYTOGENES

We purified and characterized an extracellular phospholipase produced by Listeria monocytogenes. This enzyme was separated as a homogeneous protein of 29 kDa by chromatography on DEAE-52 cellulose and Bio-Gel P100 columns. It is a zinc-dependent phospholipase C (PLC) that is mainly active at pH 6 to 7 and expresses lecithinase activity and a weaker sphingomyelinase activity. The exoenzyme also hydrolyzed phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and sphingomyelin but not phosphatidylinositol. It was distinct from the 36-kDa phosphatidylinositol PLC produced by L. monocytogenes and from the L. ivanovii sphingomyelinase. The pure protein expressed a weak, calcium-independent hemolytic activity and was not toxic in mice. Western immunoblot analysis using a rabbit immune serum raised against the enzyme showed that all virulent strains of L. monocytogenes tested produced in the culture supernatant a 29-kDa PLC. In contrast, no proteins antigenically related to the 29-kDa PLC were detected in supernatants of L. ivanovii, L. seeligeri, L. innocua, or L. welshimeri. The role in virulence of the 29-kDa PLC specifically produced by L. monocytogenes remains to be established.