NMR structure of the sterol carrier protein-2: Implications for the biological role

The determination of the NMR structure of the sterol carrier protein-2 (SCP 2), analysis of backbone N-15 spin relaxation parameters and NMR studies of nitroxide spin-labeled substrate binding are presented as a new basis for investigations of the mode of action of SCP2. The SCP2 fold is formed by a five-stranded beta-sheet and four alpha-helices. Fatty acid binding to a hy drophobic surface area formed by amino acid residues of the first and third helices, and the beta-sheet, which are all located in the polypeptide segm ent 8-102, was identified with the use of the spin-labeled substrate 16-dox ylstearic acid. Ln the free protein, the lipid-binding site is covered by t he C-terminal segment 105-123, suggesting that this polypeptide segment, wh ich carries the peroxisomal targeting signal (PTS1), might be involved in t he regulation of ligand binding. (C) 2000 Academic Press.