DNA Helicases: Hexameric Enzyme Action

Helicases are nucleoside triphosphatase-driven nanomotors that move on nucleic acid (NA) to facilitate reactions of DNA and RNA metabolic processes in the living cells. A subset of these enzymes is active as oligomeric complexes; their ring-shaped structure endows them with unique NA motor functions. The understanding of ring-shaped motor proteins is shaped by extensive biochemical and structural studies including pre-steady-state adenosine triphosphatase kinetics, single molecule NA translocation kinetics, electron microscopy, and X-ray crystallography. These studies continue to reveal the amazing coordination of conformational changes in the ring subunits prompted by nucleoside triphosphate hydrolysis that allows translocation of the NA through the central channel. In this article, we discuss the major viewpoints on the mechanisms of NA binding and translocation, active and passive mechanisms of DNA unwinding, and coordinated adenosine triphosphate hydrolysis by these motor proteins, in the light of their latest available crystal structures.