STRUCTURAL STUDIES ON MAIZE LIPID TRANSFER PROTEIN AT 1.2 Å RESOLUTION AND ITS OLEATE COMPLEX AT 1.3 Å RESOLUTION. Jae Young Lee, Dong Hae Shin, and Se Won Suh, Department of Chemistry and Center for Molecular Catalysis, Seoul National University, Seoul 151742, Korea.

The three-dimensional structures of maize lipid transfer protein (MLTP) and its complex with cis-[[Delta]]⁹-octadecenoate (oleate) have been refined with Shelxl-93 using synchrotron data The structure of uncomplexed MLTP has been refined to an R-value of 15.3 % for 19,147 reflections between 8.0 and 1.2 Å resolution and the structure of complex with oleate has been refined to an R-value 14.1% for 14,082 reflections between 8.0 and 1.3 Å resolution. The final model for uncomplexed MLTP contains all of the 93 amino acid residues, 103 water molecules, and 3 formate ions. The model for MLTP-oleate complex includes 121 water molecules, 3 formate ions, and one oleate molecule. The refined structure of MLTP at 1.2 Å resolution provides a wealth of structural details with far greater accuracy than the previous report at 1.9 Å resolution [Shin et al. (1995) Structure 3, 189-199, pdb ID code: lmzl]. A structure comparison of uncomplexed MLTP with its oleate complex demonstrated that these MLTPs show no great differences in the backbone structure, but the side chains like Asn37, Val77, and Ile83 in the portal region show above 1 Å differences. In the MLTP-oleate complex structure, the 14 carbon atoms in the tail of the oleate are buried inside the cavity and the other carbon atoms and the carboxyl group of oleate are exposed.  These atomic resolution crystal structures will provide an accurate model for protein-lipid interaction and lipid transfer mechanism.