CRYSTAL STRUCTURE OF NONSPECIFIC LIPID TRANSFER PROTEIN RICE SEEDS AT I.6 Å RESOLUTION. Kyeongsik Min, Jae Young Lee, Hoon Cha, Kwang Yeon Hwang, and Se Won Suh, Department of Chemistry, College of Natural Sciences, Seoul National University, Seoul 151-742,Korea

The crystal structure of non-specific lipid transfer protein (ns-LTP) from rice seeds, in the absence of a bound ligand, has been determined by molecular replacement using maize lipid transfer protein [Shin et al. (1995) Structure 3, 189-]99, pdb ID code: lmzl] as a starting model and refined to 1.6 Å resolution. The final model for rice ns-LTP contains all of the 91 amino acid residues, 70 water molecules, a sulfate ion, and two CAPS (3-[cyclohexylamino]-1-propanesulfonic acid) molecules. The model for rice ns-LTP has rms deviations from ideal bond lengths and angles of 0.019 Å and 1.85deg., respectively. The present crystallographic R-factor is 18.7 % for 9,420 unique reflections with F_o > 2 [[sigma]]_[[phi]] in the range 8.0-1.6 Å resolution. The structure of rice ns-LTP has a hydrophobic cavity formed by four [[alpha]]-helices similar to the previously determined structure of maize LTP. The root mean square deviation (rmsd) between them, for all common C[[alpha]] atoms, is 1.4 Å. The largest difference is in the C-terminus which moves into the hydrophobic cavity. Especially, the side chains of Tyr79 and Ile81 block the hydrophobic cavity from solvent in the portal and bottom region, respectively. The high resolution structure of rice ns-LTP provides the structural basis for understanding its function.