Understanding the physical mechanisms underlying membrane fusion requires a multi winged approach, involving model systems as well as biological membranes. We study fusion intermediates occurring in form of ordered passages or stalks connecting neighbouring bilayers in multilamellar model membrane stacks. The stalks exhibit long range crystalline order with rhombohedral symmetry in a fluid ‘host’ membrane stack, which is studied by high resolution x-ray diffraction under grazing incidence angles. Information on membrane curvature, and hydration interaction can be revealed by analyzing the quantitative electron density maps, collected for controlled environmental parameters and membrane composition [1]. Phase diagrams can be analyzed in view of stabilizing or destabilizing agents for stalk formation. While in these equilibrium phase, dehydration forces bring bilayers together favoring at some point the formation of stalks, it is specific membrane proteins and their interaction which set the local boundary conditions for membrane apposition in biological membrane fusion. In view of studying fusion in the presence of SNARE proteins, we have started a x-ray structural characterization of synaptic vesicles (SV) by small-angle x-ray scattering, and currently extent this work towards studies of SV docked to and interaction with model bilayers [2], and work towards reconstituting SNARE complexes into the stalk phase for structural analysis. [1] S. Aeffner et al., Proc.Natl.Ac.Sc.. doi: 10.1073/pnas.1119442109 (2010) [2] S. Ghosh et al., Biophys.J. 2012 Biophysical Journal (102), 1394–1402, (2012).

Structure analysis of membrane fusion by X-ray diffraction: From model membranes to organelles

251st National Meeting (2016)

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