A NOVEL CLASS OF WINGED HELIX-TURN-HELIX PROTEIN - THE DNA-BINDING DOMAIN OF MU TRANSPOSASE

Background: Mu transposase (MuA) is a multidomain protein encoded by the bacteriophage Mu genome. It is responsible for translocation of the Mu genome, which is the largest and most efficient transposon known. While the various domains of MuA have been delineated by means of biochemical methods, no data have been obtained to date relating to its tertiary structure. Results: We have solved the three-dimensional solution structure of the DNA-binding domain (residues 1-76; MuA(76)) of MuA by multidimensional heteronuclear NMR spectroscopy. The structure consists of a three-membered alpha-helical bundle buttressed by a three-stranded antiparallel beta-sheet. Helices H1 and H2 and the seven-residue turn connecting them comprise a helix-turn-helix (HTH) motif. In addition, there is a long nine-residue flexible loop or wing connecting strands B2 and B3 of the sheet. NMR studies of MUA(76) complexed with a consensus DNA site from the internal activation region of the Mu genome indicate that the wing and the second helix of the HTH motif are significantly perturbed upon DNA binding. Conclusions: While the general appearance of the DNA-binding domain of MuA(76) is similar to that of other winged HTH proteins, the connectivity of the secondary structure elements is permuted. Hence, the fold of MuA(76) represents a novel of winged HTH DNA-binding domain.