Role of charge properties of bacterial envelope in bactericidal action of human Group IIA phospholipase A2 against Staphylococcus aureus

Abstract

Mammalian Group IIA phospholipases A2 (PLA2) potently kill Staphylococcus aureus. Highly cationic properties of these PLA2 are important for Ca2+-independent binding and cell wall penetration, prerequisites for Ca2+-dependent degradation of membrane phospholipids and bacterial killing. To further delineate charge properties of the bacterial envelope important in Group IIA PLA2 action against S. aureus, we examined the effects of mutations that prevent specific modifications of cell wall (dltA) and cell membrane (mprF) polyanions. In comparison to the parent strain, isogenic dltA- bacteria are ∼30-100x more sensitive to PLA2, whereas mprF- bacteria are <3-fold more sensitive. Differences in PLA2 sensitivity of intact bacteria reflect differences in cell wall, not cell membrane, properties since protoplasts from all three strains are equally sensitive to PLA2. A diminished positive charge in PLA2 reduces PLA2 binding and antibacterial activity. In contrast, diminished cell wall negative charge by substitution of (lipo)teichoic acids with D-alanine reduces antibacterial activity of bound PLA2, but not initial PLA2 binding. Therefore, the potent antistaphylococcal activity of Group IIA PLA2 depends on cationic properties of the enzyme that promote binding to the cell wall, and polyanionic properties of cell wall (lipo)teichoic acids that promote attack of membrane phospholipids by bound PLA2.