Structural complexity and surface interactions in biomembranes: a biophysical approach

Biomembranes are complex objects made by several different molecular species. One of their most significant complexities is compositional asymmetry. Regions exist where asymmetry, both lateral and transverse, is a key factor, as in glycosphingolipids enriched rafts, where the uneven disposition is claimed to be associated to functional and structural roles. Nonetheless, membranes asymmetry is often an underestimated feature and hard to reproduce in mimics. Experimental models, bearing forced membrane leaflets asymmetry in the form of disperse aggregates in solution or of single supported bilayers, have been developed to be suitably investigated by light, neutron and x-ray scattering and reflectivity. These techniques allow to access the typical lengthscales of membranes, from the colloidal to the local, exploiting the specific advantages of the employed radiation. Neutron reflectometry and scattering allowed to access the cross structure of raft-mimes, assessing that the presence of a typical raft glycosphingolipid, GM1 ganglioside, forces asymmetry in cholesterol distribution, proving that a true coupling between the two molecules occurs [1-3]. Membranes are selective barriers and their selectivity depends on the local structure and specific composition. Multitechnique investigations allowed to address the structural response of model membranes to
approaching proteins and enzymes, such as Aβ peptides and ion channel proteins [4-6]. The possibility to create and study customized membranes mimicking different membrane portions opens the way to the detailed investigation of a variety of specific molecule-membrane interactions.

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[2] V. Rondelli et al., Biochimica et Biophysica Acta- Biomembranes 1818, 2860 (2012)
[3] V. Rondelli et al., Journal of Physics 340, 012083 (2012)
[4] V. Rondelli et al., Scientific Reports 6, 20997 (2016)
[5] V. Rondelli et al., Biochimica et Biophysica Acta-Biomembranes 1859, 5 (2017)
[6] V. Rondelli et al., Biochimica et Biophysica Acta- General Subjects 18562, 1742 (2018)