Abstract
Apolipoprotein (apo) E regulates plasma lipid homeostasis through its ability to interact with the low density lipoprotein (LDL) receptor family. Whereas apoE is not a ligand for receptor binding in buffer alone, interaction with lipid confers receptor recognition properties. To investigate the nature of proposed lipid binding-induced conformational changes in apoE, we employed multidimensional heteronuclear NMR spectroscopy to determine the structure of an LDL receptor-active, 58-residue peptide comprising residues 126-183 of apoE in association with the micelle-forming lipid dodecylphosphocholine (DPC). In the presence of 34 mm DPC the peptide forms a continuous amphipathic helix from Glu131 to Arg178. NMR relaxation studies of DPC-bound apoE-(126-183), in contrast to apoE-(126-183) in the presence of TFE, are consistent with an isotropically tumbling peptide in solution giving a global correlation time of approximately 12.5 ns. These data indicate that the helical peptide is curved and constrained by a lipid micelle consisting of approximately 48 DPC molecules. Although the peptide behaves as if it were tumbling isotropically, spectral density analysis reveals that residues 150-183 have more motional freedom than residues 134-149. These molecular and dynamic features are discussed further to provide insight into the structural basis for the interaction between apoE and the ligand binding repeats of the LDL receptor.
Highlights
Biophysical studies reveal that apoE is comprised of two structural domains, a 22-kDa N-terminal (NT) domain and a 10-kDa C-terminal domain [4, 5]
The N- and C-terminal domains are connected by a flexible, unstructured, region encompassing amino acids 191–216 that is susceptible to proteolytic cleavage
Complexation with phospholipids results in a particle that binds efficiently to the LDL receptor [6]. These data indicate that a lipid binding-induced conformational adaptation of apoE, which can be mimicked by the isolated NT domain, is an essential feature action between apoE and the ligand binding repeats of of apoE function as a ligand for receptor-mediated endocytosis the LDL receptor
Summary
69.6 Ϯ 1.4 Ebonds, 15.2 Ϯ 0.6 Eangles, 47.1 Ϯ 1.2 EVDW, 0.14 Ϯ 0.24 ENOE, 2.4 Ϯ 0.5 Edihedral, 0.3 Ϯ 0.1. ApoE3-(126 –183) efficiently transforms anionic phospholipid vesicles into LDL receptor competent, peptide-lipid complexes. Analysis of these complexes by electron microscopy revealed disc-shaped particles with an average diameter of 13 Ϯ 3 nm. The structure of this receptor-active apoE peptide was determined by NMR experiments conducted in the presence of the lipid mimetic cosolvent trifluoroethanol (TFE) [20]. In 50% TFE, apoE-(126 –183) forms a continuous amphipathic ␣-helix over residues Thr130–Glu179 To extend these findings and investigate the structural organization of apoE-(126 –183) in the presence of lipid, we have determined the structure of apoE-(126 –183) in complex with the micelleforming single acyl chain phospholipid dodecylphosphocholine (DPC). The results are discussed in terms of structural determinants responsible for apoE conformational adaptability and binding to the LDL receptor family
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call