Structural investigations of native and oxidised LDL using X-ray and neutron solution scattering techniques

Abstract
The gross structures of both the native and oxidised (atherogenic) forms of low density lipoproteins (LDL) were compared using neutron and X-ray solution scattering. Neutron data in ²H₂O solutions showed that native LDL is well represented as a quasispherical structure, while X-ray data showed that the internal structure of LDL has lipid in the core and apo-B100 protein and phospholipid headgroups on the surface. When LDL oxidation was induced using a ratio of 6.4 µM Cu²⁺ to 1 mg/ml LDL protein, structural disintegration of LDL was observed in the scattering curves over a 72 hour period. This disintegration was parallelled by an increase in the R_G and I(0)/c parameters observed by neutron and X-ray Guinier analyses, and changes in the concentric shell-like structure of the lipids in the core as observed in the distance distribution functions. Structural changes included the aggregation and degradation of LDL, as confirmed by subsequent SDS-polyacrylamide gel elctrophoresis. These changes occurred after the antioxidant content of LDL had been fully depleted.