Overcoming the speed limit of four-way DNA branch migration with bulges in toeholds

Dynamic DNA nanotechnology involves the use of DNA strands to create programmable reaction networks and nanodevices. The key reaction in dynamic DNA nanotechnology is the exchange of DNA strands between different molecular species, which is achieved through three-way and four-way DNA exchange reactions. While both of these reactions have been widely used to build reaction circuits, the four-way exchange reaction has traditionally been slower and less efficient than the three-way reaction. In this paper, we describe a new mechanism to optimise the kinetics of the four-way DNA exchange reaction by adding bulges to the toeholds of the four-way DNA complexes involved in the reaction. These bulges facilitate an alternative branch migration mechanism and destabilise the four-way DNA junction, increasing the branch migration rate and unbinding rate of the four-way exchange reaction, bringing it closer to the kinetics of the three-way reaction. This new mechanism has the potential to expand the field of dynamic DNA nanotechnology by enabling efficient four-way DNA exchange reactions for in vivo applications.