Secondary structure of human apolipoprotein A-I(1-186) in lipid-mimetic solution

The solution structure of an apoA-I deletion mutant, apoA-I(1-186) was determined by the chemical shift index (CSI) method and the torsion angle likelihood obtained from shift and sequence similarity (TALOS) method, using heteronuclear multidimensional NMR spectra of u-(13)C, u-(15)N, u-50% (2)H]apoA-I(1-186) in the presence of sodium dodecyl sulfate (SDS). The backbone resonances were assigned from a combination of triple-resonance data (HNCO, HNCA, HN(CO)CA, HN(CA)CO and HN(COCA)HA), and intraresidue and sequential NOEs (three-dimensional (3D) and four-dimensional (4D) 13C- and 15N-edited NOESY). Analysis of the NOEs, H(alpha), C(alpha) and C' chemical shifts shows that apoA-I(1-186) in lipid-mimetic solution is composed of alpha-helices (which include the residues 8-32, 45-64, 67-77, 83-87, 90-97, 100-140, 146-162, and 166-181), interrupted by short irregular segments. There is one relatively long, irregular and mostly flexible region (residues 33-44), that separates the N-terminal domain (residues 1-32) from the main body of protein. In addition, we report, for the first time, the structure of the N-terminal domain of apoA-I in a lipid-mimetic environment. Its structure (alpha-helix 8-32 and flexible linker 33-44) would suggest that this domain is structurally, and possibly functionally, separated from the other part of the molecule.