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Nanostructure characterization of planar biomimetic membranes with neutron reflectometry

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I will present neutron reflectometry (NR) data on model biological membranes systems to point out how a biophysical approach can help address specific biological problems. In the first example I will describe a structural characterization of floating lipid bilayers in the presence of gold nanoparticles in the context of nano toxicity. The development of novel nano-engineered materials poses important questions on how these new materials will interact with living systems. On the one hand, possible adverse effects must be assessed in order to prevent risks for health and environment [1]. On the other hand, the understanding of how these materials interact with biological systems might result in the creation of novel biomedical applications [2]. I will show NR experiments performed on zwitterionic DSPC and two-component negatively charged DSPC /DSPG double bilayers in the presence of gold nanoparticles (NP) functionalized with cationic and anionic head groups. Structural information was obtained that provided insight into the fate of the NPs with regard to the integrity of the model cell membranes. The information obtained might influence the strategy for a better nanoparticle risk assessment based on a surface charge evaluation and contribute to nano-safety considerations already during their design. In the second example, I will provide insight into the nano-scale structure of OprF protein embedded in tethered lipid bilayers. OprF is the major porin of the outer membrane of the PseudomonaAeuruginosa bacterium and it is a very novel target for new drugs that will kill bacteria resistant to standard antibiotics. The crystallographic high-resolution structure of OprF is not available due to the difficulties involved in crystallising membrane proteins. By the use of neutron reflectometry, we provided an alternative route to obtain fundamental low-resolution information on the nanoscale structure OprF, in an environment that mimics its native condition. NR allowed us to characterize the nanostructural details of the lipid membrane, the amount of the protein embedded in the bilayer, the thickness and the orientation of the extramembrane domain of the proteins, which extends from the membrane. These investigations are not possible using the classical techniques of biology and reinforce the crucial role played by neutron scattering in evincing fundamental details of biological samples.This study showed that OprF made using the cell free protocol and incorporated into tethered lipid bilayer provides a controllable (and measurable at the nanoscale) biomimetic system constructed in vitro.

[1] Maynard, A.D. Nanotechnology: a Strategy for Addressing Risk; Woodrow Wilson International Center for Scholars: Washington, DC, (2006). [2] Murphy,C.J.; Gole, A.M.;Stone, J.W. Acc. Chem. Res. (2008), 41, 1721–1730. [3] Tatur, S.; Maccarini, M.; Barker, R.; Fragneto, G.; Langumir (2013) 29 (22), 6606

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