Double-stranded DNA translocation: structure and mechanism of hexameric FtsK.
FtsK is a DNA translocase that coordinates chromosome segregation and cell division in bacteria. In addition to its role as activator of XerCD site-specific recombination, FtsK can translocate double-stranded DNA (dsDNA) rapidly and directionally and reverse direction. We present crystal structures of the FtsK motor domain monomer, showing that it has a RecA-like core, the FtsK hexamer, and also showing that it is a ring with a large central annulus and a dodecamer consisting of two hexamers, head to head. Electron microscopy (EM) demonstrates the DNA-dependent existence of hexamers in solution and shows that duplex DNA passes through the middle of each ring. Comparison of FtsK monomer structures from two different crystal forms highlights a conformational change that we propose is the structural basis for a rotary inchworm mechanism of DNA translocation.