title: Electron paramagnetic resonance spectroscopy of site-directed spin labels reveals the structural heterogeneity in the N-terminal domain of apoA-I in solution.
abstract: Apolipoprotein A-I (apoA-I) is the major protein constituent of high density lipoprotein (HDL) and plays a central role in phospholipid and cholesterol metabolism. This 243-residue long protein is remarkably flexible and assumes numerous lipid-dependent conformations. Consequently, definitive structural determination of lipid-free apoA-I in solution has been difficult. Using electron paramagnetic spectroscopy of site-directed spin labels in the N-terminal domain of apoA-I (residues 1-98) we have mapped a mixture of secondary structural elements, the composition of which is consistent with findings from other in-solution methods. Based on side chain mobility and their accessibility to polar and non-polar spin relaxers, the precise location of secondary elements for amino acids 14-98 was determined for both lipid-free and lipid-bound apoA-I. Based on intermolecular dipolar coupling at positions 26, 44, and 64, these secondary structural elements were arranged into a tertiary fold to generate a structural model for lipid-free apoA-I in solution.
authors.affiliation: Department of Biochemistry, University of California, Davis, California 95616, USA.
authors.forename: Jens O
authors.initials: JO
authors.lastname: Lagerstedt
authors.forename: Madhu S
authors.initials: MS
authors.lastname: Budamagunta
authors.forename: Michael N
authors.initials: MN
authors.lastname: Oda
authors.forename: John C
authors.initials: JC
authors.lastname: Voss
mesh_terms: D016632:Apolipoprotein A-I / Q000737:chemistry*; D003460:Crystallization; D019281:Dimerization; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D006801:Humans; D008055:Lipids / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D016296:Mutagenesis; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013113:Spin Labels
chemical_list: D016632:Apolipoprotein A-I; D008055:Lipids; D013113:Spin Labels