Structure and mechanism of the RuvB Holliday junction branch migration motor

The RuvB hexamer is the chemomechanical motor of the RuvAB complex that mig rates Holliday junction branch-points in DNA recombination and the rescue o f stalled DNA replication forks. The 1.6 Angstrom crystal structure of Ther motoga maritima RuvB together with five mutant structures reveal that RuvB is an ATPase-associated with diverse cellular activities (AAA + -class ATPa se) with a winged-helix DNA-binding domain. The RuvB-ADP complex structure and mutagenesis suggest how AAA + class ATPases couple nucleotide binding a nd hydrolysis to interdomain conformational. changes and asymmetry within t he RuvB hexamer implied by the crystallographic packing and small-angle X-r ay scattering in solution. ATP-driven domain motion is positioned to move d ouble-stranded DNA through the hexamer and drive conformational changes bet ween subunits by altering the complementary hydrophilic protein-protein int erfaces. Structural and biochemical analysis of five motifs in the protein suggest that ATP binding is a strained conformation recognized both by sens ors and the Walker motifs and that intersubunit activation occurs by an arg inine finger motif reminiscent of the GTPase-activating proteins. Taken tog ether, these results provide insights into how RuvB functions as a motor fo r branch migration of Holliday junctions. (C) 2001 Academic Press.