FtsK in motion reveals its mechanism for double-stranded DNA translocation

Abstract

FtsK protein contains a fast DNA motor involved in bacterial chromosome dimer resolution. To understand how FtsK moves DNA, we solved the 3.6 [A] resolution cryo-EM structure of the motor domain of FtsK while translocating double-stranded DNA. Each subunit of the hexameric ring adopts a unique conformation and one of three nucleotide states. Two DNA-binding loops within four subunits form a pair of spiral staircases within the ring, interacting with the two DNA strands. This suggests that simultaneous conformational changes in all ATPase domains at each catalytic step generate movement through a mechanism related to filament treadmilling. While the ring is only rotating around the DNA slowly, it is instead the conformational states that rotate around the ring as the DNA substrate is pushed through.