STUDY OF THE EFFECTS OF BMP LIPID PRESENCE ON MEMBRANE MODELS

Lysosomes and endosomes are cellular organelles composed of a single heterogeneous membrane. These organelles have the capacity to generate compartments that play a crucial role along the endocytic process. BMP (bis(monoaclyglycero)phosphate) is one of the main lipids that compose these membrane compartments, with biological functions widely studied. In order to contribute to the understanding of this lipid properties, small angle X-ray scattering (SAXS) and optical microscopy experiments using BMP-containing membrane models were performed along with atomistic simulations of bilayer composed by this lipid.

The main objective is to find out a relation between the multivesicular bodies formation considering different proportions of BMP on binary membranes (POPC:BMP, where POPC is 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine), investigating the influence of an acidic pH (4.5 is the pH inside of late endosomes) in comparison of a neutral one (7.4) with the same Britton-Robinson buffer. To complement the experimental analysis, molecular dynamics simulations (MD) were employed here too.

Classical atomistic simulations were performed using GROMACS. Force fields CHARMM-GUI was adopted. Bilayers with different lipid compositions were studied, including a structural isomer of BMP, namely DOPG (1,2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol)) and protonated and deprotonated BMP. SuAVE software was also used for some analysis. For microscopy and SAXS measurements, GUVs (growth by gel method) and LUVs (obtained by extrusion method) were assayed, respectively .

Lipid properties such as average area per lipid head, order parameter, electron density profiles, hydration level, for instance, will be discussed in the light of MD results in comparison to model fitting to the SAXS data. Experimental and theoretical data walk alongside for a better understanding of nature, including at an atomic level.