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)

Abstract

We report the 2.3 Å resolution X-ray crystal structure of the GDP-bound form of the RanQ69L mutant that is used extensively in studies of nucleocytoplasmic transport and cell-cycle progression. When the structure of GDP-RanQ69L from monoclinic crystals with P2₁ symmetry was compared with the structure of wild-type Ran obtained from monoclinic crystals, the Q69L mutant showed a large conformational change in residues 68–74, which are in the switch II region of the molecule which changes conformation in response to nucleotide state and which forms the major interaction interface with nuclear 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, solution binding studies were unable to detect any interaction between NTF2 and GDP-RanQ69L under conditions where GDP-Ran bound effectively. This interaction between NTF2 and GDP-Ran is required for efficient nuclear protein import and may function between the docking and translocation steps of the pathway.