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 intraresi- due and sequential NOEs (three-dimensional (3D) and four- dimensional (4D) 13 C- and 15 N-edited NOESY). Analysis of the NOEs, H K ,C K and CP chemical shifts shows that apoA-I(1^186) in lipid-mimetic solution is composed of K-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 (K-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. fl 2001 Federation of European Bio- chemical Societies. Published by Elsevier Science B.V. All rights reserved.