In Situ Atomic Force Microscope Imaging of Supported Lipid Bilayers

Abstract

In situ AFM images of phospholipase A 2 (PLA 2 ) hydrolysis of mica-supported one-and two-component lipid bilayers are presented. For one-component DPPC bilayers an enhanced enzymatic activity is observed towards preexisting defects in the bilayer. Phase separation is observed in two-component DMPC-DSPC bilayers and a remarkable enhanced hydrolytic activity of the PLA 2 -enzyme for the DMPC-rich phase is seen. Furthermore, in a supported double bilayer system a characteristic ripple structure, most likely related to the formation of the P β' -ripple phase is observed.

Coupling of the Orientations of Thermotropic Liquid Crystals to Protein Binding Events at Lipid-Decorated Interfaces

“…We also note that past studies have demonstrated that PLA 2 partially extracts lipids from an interface prior to cleavage. [54][55][56][57][58][59] It is possible that the…”

Rational Design of a Liposomal Drug Delivery System Based on Biophysical Studies of Phospholipase A 2 Activity on Model Lipid Membranes

“…This general picture of sPLA 2 activation is supported by detailed analyses of atomic force microscopy images of solid-supported bilayers in the presence of sPLA 2 in the various stages before and after the lag phase [30,33,34]. These analyses strongly suggest that sPLA 2 attacks at areas with structural defects, such as domain boundaries, at regions with accumulated hydrolysis products, and at the edges of pre-existing holes in the bilayer.…”

“…Determination of the lateral organization of liposomal membranes on scales ranging from 10 to 1000 nm has proved elusive [27][28][29][30]. However, indirect and direct evidence from recent studies of model membranes as well as biological membranes has suggested that membranes are laterally heterogeneous and structured in terms of domains and so-called rafts [31].…”

“…Lipid-domain formation caused by cooperative phenomena in the lipid bilayers is particularly important for the activation of sPLA 2 [32][33][34][35]. The cooperative phenomena in lipid bilayers are caused by the fundamental interactions between the lipid molecules and are a consequence of the many-particle character of the supramolecular aggregate.…”

“…increasing curvature [46], and therefore larger curvature tension. For bilayers made of lipids with different chain lengths, although sPLA 2 seems to bind uniformly across solid and fluid domains enriched in the long-and short-chain lipid species, respectively, the enzyme prefers the short-chain lipid species, which is hydrolyzed first [30,35,47]. The preferred hydrolysis of the short-chain lipids, which are in the fluid phase, might be due to the lower surface area density of the lipid head groups in this phase.…”