Three-dimensional structure in solution of a wheat lipid-transfer protein from multidimensional 1H-NMR data. A new folding for lipid carriers.

Two-dimensional and three-dimensional 1H-NMR experimental data [Simorre, J. P., Caille, A., Marion, D., Marion, D. & Ptak, M. (1991) Biochemistry 30, 11600-11608] were used to build models of the three-dimensional structure of a non-specific wheat lipid-transfer protein (LTP) by using distance geometry, simulated annealing, energy minimization and molecular dynamics techniques. A first set of 881 distance constraints derived from NOE cross-peak intensities was used to generate 74 initial structures. One family of topological mirror images of the protein structure was eliminated by considering helical secondary-structure organization and steric requirements. Back calculations of NOE intensities led us to introduce 535 additional distance constraints. Finally, 21 structures were selected as representative of the structure of the protein. The polypeptide backbone folds into a simple and original right-handed winding. It is composed of a bundle of four helices linked by flexible loops, which is packed against a C-terminal fragment forming a non-standard saxophone-like shape. The folded protein is stabilized by hydrophobic interactions and the four disulfide bridges combined by pairs on each side of the protein. An hydrophobic cleft, formed by residues located in the second half of the protein could be a potential site for the binding of lipids.