Free Energies of Interaction of Lipids with Regulatory Binding Sites on the Transmembrane Domain of the EGF Receptor

Abstract

The structural impact of high hydrostatic pressure (HHP) was studied with different types of LDL (native, oxidized and triglyceride rich) with SANS (PSI, Switzerland) and SAXS (Elettra, Italy). The HHP ranged from 50 to 3000 bar. Temperature points were chosen below, on and above T m. The pair distance distribution functions p(r) of the SAS curves revealed pressure dependent changes of the particle structure seen in the low q-region (~0.25 nm À1), also reflected by a decrease of Radii of Gyration (R g) with increasing pressure. Especially the p(r) functions from the SAXS data do not only show an overall particle change but also a highly pressure sensitive inner organization. A triplepeak feature indicating the lamellar lipid organization below T m was induced by raising the pressure up to 3000 bar. These pressure sensitive lipid layers were observed by scattering intensity changes in SAXS curves at q=1.7 nm À1. The shape alterations could be evidenced by fitting an ellipsoidal model to the SANS curves resulting in a decrease of the ellipsoidal radii under pressure. A new LDL model considering the cross-sectional electron density profile is developed and applied to the SAS data to get a more detailed insight into pressure dependent behavior.