Molecular virulence mechanism of phospholipase C of Pseudomonas aeruginosa

Bacterial phospholipases form a structurally heterogeneous group of lipolytic enzymes that hydrolyze one or more ester bonds in their substrates. Many of these enzymes are essential virulence factors required for the efficient infection of human or animal host cells. Pseudomonas aeruginosa secrets two virulent glycerophospholipases of type C (PLC N and PLC H), the latter of which has hemolytic activity on red blood cells. Cryo-electron microscopy and X-ray crystallography analysis showed that both proteins have two domains with similar tertiary structures, conserved active site residues, and surprisingly the phosphorylation of the active side threonine that acts as the nucleophile in lipase activity. Docking analysis suggests that the distinct substrate preference of PLC N for phosphatidylserine and PLC H for phosphatidylcholine is mainly caused by electrostatic differences in the substrate binding pocket. Further time-resolved studies using atomic force microscopy (AFM) showed how PLC H can damage host membranes by forming large pores in lipid bilayers within minutes.