Characterization of the structure of polydisperse human low-density lipoprotein by neutron scattering

Abstract

Low-density lipoproteins (LDL) in plasma are constructed from a single molecule of apolipoprotein B-100 (M(r) 512000) in association with lipid (approximate M(r) 2-3 x 10(6)). The gross structure was studied using an updated pulsed-neutron camera LOQ with an area detector to establish the basis for the interpretation of structural changes seen during dynamic studies of LDL oxidation. Neutron-scattering data for LDL in 100% 2H2O buffers emphasize their external appearance. Guinier analysis on a continuous-flux neutron camera D17 revealed pronounced concentration-dependences in the radius of gyration, RG, and the intensity of forward scattering, I(0) (equivalent to the M(r) of LDL) between 0.5 and 11 mg of LDL protein/ml. LDL preparations from different donors gave different RG values. When extrapolated to zero concentration, RG values ranged between 8.3 and 10.6 nm and were linearly correlated with M(r), which is consistent with a spherical structure. The distance-distribution function P(r) in real space showed a single maximum at 9.1-10.9 nm, which is just under half the observed maximum dimension of 23.1 +/- 1.2 nm expected for a spherical structure. The neutron radial-density function p(r) exhibited a plateau of high and featureless density at the centre of LDL. LDL can be modelled by a polydisperse assembly of spheres with two internal densities and a mean radius close to 10.0 nm in a normal distribution of radii with a standard deviation of 2.0 nm. The data are consistent with recent electron-microscopy and ultracentrifugation data.(ABSTRACT TRUNCATED AT 250 WORDS)

Time-course studies by synchrotron X-ray solution scattering of the structure of human low-density lipoprotein during Cu2+-induced oxidation in relation to changes in lipid composition

“…Accordingly, X-ray data from a concentration series of native LDLs are presented, and the effect of LDL polydispersity on Xray-scattering curves are assessed. This complements the analyses of native LDLs by neutron scattering [13]. Next, X-ray-scattering data for LDLs undergoing oxidation under the same conditions used in neutron oxidation studies [11] are presented.…”

“…LDLs (density range 1.025-1.055 g\ml) were isolated by ultracentrifugation, and protein concentrations were determined as described previously [11,13]. LDLs were dialysed against 12.5 mM Tris\140 mM NaCl, pH 7.4, in water solvents for both X-ray scattering and biochemical experiments.…”

“…At low Q values, Figure 1 illustrates how satisfactory linear Guinier fits in a Q:R G range between 0.7 and 1.7 were obtained in a total of 187 LDL data acquisitions. Because of the larger X-ray R G values and the need to retain a Q:R G range similar to that used with neutron data [13], the fitted Q range is now reduced to 0.06-0.13 nm −" , sometimes 0.10-0.13 nm −" in place of the Q range of 0.08-0.19 nm −" used for neutron analyses. Statistical errors of p0.2 nm in the R G values at 10.9 mg\ml, rising to as much as p1 nm at 0.9 mg\ml, were encountered in the X-ray R G analyses (results not shown), as it is necessary to work at low Q close to the main beam where background levels are increased.…”

“…The joint use of neutron and X-ray solution scattering offers complementary but different views of the structure of LDL [12]. Neutron data on LDL in 100 % #H # O buffers monitor the external appearance of a polydisperse spherical structure of almost uniform scattering density [13]. X-ray scattering monitors the internal structure of LDLs in solution, since their lipid and protein components have different scattering densities which permits these to be readily distinguished from each other [14].…”

Modeling the Interaction of Peroxynitrite with Low-density Lipoproteins. II: Reaction/Diffusion Model of Peroxynitrite in Low-density Lipoprotein Particles

“…This layer contains free cholesterol and a protein molecule, apolipoprotein B-100 which is recognized by receptors in the liver and in cell membranes. The core of the cell consists of triglycerols and cholesteryl esters (Kroon, 1994;Meyer et al, 1995b;van Antwerpen et al, 1997).…”