Soluble complex formation between low-density lipoprotein and glycosaminoglycans. A 2H and 31P-NMR, and quasi-elastic light scattering study

Abstract

Soluble complex formation between LDL and heparin (HEP) and chondroitin sulfate (CS) has been studied by 2H- and 31P-NMR and light scattering. The 2H-NMR linewidths of [ 2H]HEP and [ 2H]C4S increase substantially upon binding to LDL, with the [ 2H]HEP linewidths broader at low glycosaminoglycan (GAG)/low density lipoprotein (LDL) ratios. Preliminary analysis of the bound C 2H 3 group correlation times suggests that the observed linewidths are determined by the complex size, and that both [ 2H]GAGs have similar motions when bound to LDL. The 31P-NMR data demonstrate that large LDL-HEP complexes (diameter approx. 50 nm) are formed only over a narrow range of HEP concentrations, whereas the size of LDL-CS complexes increases continuously over the range of CS concentrations studied, reaching values of 32–35 nm for both C4S and C6S. At the lower protein concentrations studied by light scattering (⩽1 mg/ ml), the same trends are observed, although the mean diameters are less than those estimated by 31P-NMR. Soluble complex formation was unaffected by the presence of 2 mM Ca 2+. Dilution studies demonstrate that complex size varies with protein concentration. The binding of GAGs to LDL was also examined by HEP-CS competition studies. HEP has the higher affinity while no differences in binding could be detected between C4S and C6S.