Lipid protrusions, membrane softness, and enzymatic activity

The activity of phospholipase A(2) on lipid bilayers displays a characteristic lag burst behavior that has previously been shown to reflect the physical properties of the substrate. It has remained unclear which underlying molecular mechanism is responsible for this phenomenon. We propose here that protrusions of single lipid molecules out of the bilayer plane could provide such a mechanism. The proposal is supported by a combination of atomic-scale molecular dynamics simulations, theory, and experiments that have been performed in order to investigate the relationship between on the one side lipid protrusion modes and mechanical softness of phospholipid bilayers and on the other side the activity of enzymes acting on lipid bilayers composed of different unsaturated lipids. Specifically, our experiments show a correlation between the bilayer bending rigidity and the apparent Arrhenius activation energy extracted from systematic lag-time versus temperature analyses.