Multiple phospholipid substrates of phospholipase C/sphingomyelinase HR2 from Pseudomonas aeruginosa

The activity of phospholipase C/sphingomyelinase HR2 (PlcHR2) from Pseudomonas aeruginosa was characterized on a variety of substrates. The enzyme was assayed on liposomes (large unilamellar vesicles) composed of PC:SM:Ch:X (1:1:1:1; mol ratio) where X could be PE, PS, PG, or CL. Activity was measured directly as disappearance of substrate after TLC lipid separation. Previous studies had suggested that PlcHR2 was active only on PC or SM. However we found that, of the various phospholipids tested, only PS was not a substrate for PlcHR2. All others were degraded, in an order of preference PC > SM > CL > PE > PG. PlcHR2 activity was sensitive to the overall lipid composition of the bilayer, including non-substrate lipids.