A drastic conformational change in the trans-activation motif observed in the crystal structure of the disulfide cross-linked Fis V13C mutant

Wei-Zeng Yang (楊維仁), Li-Chu Tsai (蔡麗珠) and Hanna S. Yuan (袁小琀)

Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan, ROC.

中央研究院 分子生物研究所

 

                    Fis protein was first discovered by its critical role in stimulating site-specific DNA inversions in enteric bacteria.  Our previous X-ray crystal structure analyses of wild-type and mutant Fis proteins reveal that Fis contains a N-terminal mobile b-hairpin arms where is the trans-activation region responsible for direct interactions with invertases.  In order to better understand the structural and functional roles for the residues located in this region, we have resolved the crystal structures of a series of Fis N-terminal mutants, including V13C T15C, V16C, Q21C, D20K, H22V, and S18C/K36E.

                     In all these mutant structures, the disulfide cross-linked V13C reveals an unexpected drastic conformational change in the trans-activation region.  V13C is active in the reduced form and inactive in the oxidized form in the Hin catalyzed DNA inversion reaction.  The crystal structure of the oxidized V13C, solved by molecular replacement methods, shows that the two b-strands in the b-hairpin arms are detached resulting in a movement more than 15 Å for the Ca-atom at 13 position.  This result suggests that a b-hairpin structure is likely retained in inversion and demonstrates that the trans-activation motif in Fis is highly flexible that it can adopt different conformations.