Interactions of two structurally related anionic phospholipids cardiolipin and phosphatidylglycerol with...

Anionic phospholipids cardiolipins (CL) and phosphatidylglycerols (PG) dominate in the biomembranes of the majority of soil bacteria. CL to PG ratio differs between the species and is also dependent on the external conditions. CL/PG ratio is different in polluted than in unspoiled soils and it was hypothesized that it is connected with the activity of the membranelytic enzymes from the phospholipase A2 class (PLA2) as it was proved that persistent soil pollutants can activate PLA2. In our studies we applied the Langmuir monolayer technique and Brewster angle microscopy to elucidate the mechanism of the interactions of PLA2 with the model membranes formed by anionic phospholipids. It turned out that there are significant differences between CL and PG. The monolayer of PG is hydrolyzed readily and entirely, whereas for CL approximately 30% of the phospholipid molecules are hydrolyzed after which the enzyme is inhibited. The observed differences between PG and CL are strictly connected with the hydrophobicity of the generated lysolipids: lyso-PG and lyso-CL. Lyso-PG is water soluble and leaves the interface whereas lyso-CL is water-insoluble remains at the interface and modifies the monolayer properties. The second hydrolysis product - myristic acid (MA) forms crystallites of calcium myristate when generated from PG, whereas when generated from CL it is shielded by the lysolipid and does not interact with calcium. Therefore, on the basis of our study it can be concluded that the increase in CL content protects the soil bacteria from PLA2 activity and from the loss of calcium homeostasis.