The structure of the Q69L mutant of GDP-Ran shows a major conformational change in the switch II loop that accounts for its failure to bind nuclear transport factor 2 (NTF2)

We report the 2.3 Angstrom resolution X-ray crystal structure of the GDP-bo und form of the RanQ69L mutant that is used extensively in studies of nucle ocytoplasmic transport and cell-cycle progression. When the structure of GD P-RanQ69L from monoclinic crystals with P2(1) symmetry was compared with th e structure of wild-type Ran obtained from monoclinic crystals, the Q69L mu tant showed a large conformational change in residues 68-74, which ape in t he switch II region of the molecule which changes conformation in response to nucleotide state and which forms the major interaction interface with nu clear transport factor 2 (NTF2, sometimes called p10). This conformational change alters the positions of key residues such as Lys71, Phe72 and Arg76 that are crucial for the interaction of GDP-Ran with NTF2 and indeed, solut ion binding studies were unable to detect any interaction between NTF2 and GDP-RanQ69L under conditions where GDP-Ran bound effectively. This interact ion between NTF2 and GDP-Ran is required for efficient nuclear protein impo rt and may function between the docking and translocation steps of the path way. (C) 1998 Academic Press.