New tools for the structural characterization of biomembrane systems

RAFAEL GUSTAVO OLIVEIRA

Congreso; 46th Congress of the Brazilian Society of Biophysics (SBBf) / LAFESB,51th Annual Meeting of the Brazilian Society of Biochemistry and Molecular Biology (SBBq); 2022

New emerging techniques will be allowing the experimental determination of structural parameters in membrane systems at the South Cone over the next years. First, the Laboratorio Argentino de Haces de Neutrones (LAHN) is planning for the second round of instrumentation a Neutron Reflectometer and two Small Angle Neutron Scattering instruments. I give an example (measured by our group at the Institute Laue Langevin, Grenoble) of the kind of experiments that will be performed at LAHN with lipid multilayers in humidity-temperature chambers. With this setup also mechanical parameters (like bending rigidity and compressibility) are obtained by analyzing the off-specular scattering. The neutron reflectometer also will allow the positioning of horizontal (liquid samples), then Langmuir troughs are planned for this instrument. SANS will allow for the same kind of measurements in isotropic systems, just like SAXS, but with contrast matching in scattering length density (analogous to electron density in X-ray experiments. Altogether, these efforts will cover different systems from monolayer to bi- and multi-layers, in a set of variable environmental conditions, like temperature, osmotic pressure, lateral pressure, chemical and isotopical composition, etc). Additionally, in our lab we have developed new measurements of quantitative reflectivity on Langmuir monolayers in a Brewster angle microscope (BAM). By contrast matching (as in neutron scattering) we experimentally determine the refractive index of the film, which combined with reflectivity allow us to calculate the thickness of the films. In order to evaluate what kind of thickness is actually measured, the results from BAM were compared to the ones determined by GIXOS (Grazing Incidence X-ray Off Specular Scattering). The last is a setup that allows the determination of the perpendicular structure of the monolayer at the Laboratorio Nacional de Luz Sincrotron (Campinas). The comparison of GIXOS and BAM thicknesses, permits us to conclude that the BAM setup measures the global thickness of the lipid monolayer.