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* MEMPHYS-Center for Biomembrane Physics, Department of Chemistry, and LiPlasome Pharma A/S, Technical University of Denmark, DK-2800 Lyngby, Denmark; and Department of Physics, University of Southern Denmark, DK-5230 Odense M, Denmark
Correspondence: Address reprint requests to Chad Leidy, MEMPHYS-Center for Biomembrane Physics, Technical University of Denmark, Dept. of Chemistry, Bldg. 206, DK-2800 Lyngby, Denmark. Tel.: 45-4525-2431; Fax: 45-4588-3136; E-mail: cleidy{at}kemi.dtu.dk.
The sensitivity of phospholipase A2 (PLA2) for lipid membrane curvature is explored by monitoring, through time-resolved atomic force microscopy, the hydrolysis of supported double bilayers in the ripple phase. The ripple phase presents a corrugated morphology. PLA2 is shown to have higher activity toward the ripple phase compared to the gel phase in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) membranes, indicating its preference for this highly curved membrane morphology. Hydrolysis of the stable and metastable ripple structures is monitored for equimolar DMPC/1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)-supported double bilayers. As shown by high-performance liquid chromatography results, DSPC is resistant to hydrolysis at this temperature, resulting in a more gradual hydrolysis of the surface that leads to a change in membrane morphology without loss of membrane integrity. This is reflected in an increase in ripple spacing, followed by a sudden flattening of the lipid membrane during hydrolysis. Hydrolysis of the ripple phase results in anisotropic holes running parallel to the ripples, suggesting that the ripple phase has strip regions of higher sensitivity to enzymatic attack. Bulk high-performance liquid chromatography measurements indicate that PLA2 preferentially hydrolyzes DMPC in the DMPC/DSPC ripples. We suggest that this leads to the formation of a flat gel-phase lipid membrane due to enrichment in DSPC. The results point to the ability of PLA2 for inducing a compositional phase transition in multicomponent membranes through preferential hydrolysis while preserving membrane integrity.
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