MAJOR DOMAIN SWIVELING REVEALED BY THE CRYSTAL-STRUCTURES OF COMPLEXES OF ESCHERICHIA-COLI REP HELICASE BOUND TO SINGLE-STRANDED-DNA AND ADP

Crystal structures of binary and ternary complexes of the E. coli Rep helicase bound to single-stranded (ss) DNA or ssDNA and ADP were deter mined to a resolution of 3.0 Angstrom and 3.2 Angstrom, respectively. The asymmetric unit in the crystals contains two Rep monomers differin g from each other by a large reorientation of one of the domains, corr esponding to a swiveling of 130 degrees about a hinge region. Such dom ain movements are sufficiently large to suggest that these may be coup led to translocation of the Rep dimer along DNA. The ssDNA binding sit e involves the helicase motifs la, Iii, and V, whereas the ADP binding site involves helicase motifs I and IV. Residues in motifs II and VI may function to transduce the allosteric effects of nucleotides on DNA binding. These structures represent the first view of a DNA helicase bound to DNA.