Using Magnetic Tweezers to Unravel the Mechanism of the G-Quadruplex Binding and Unwinding Activities of DHX36 Helicase.

Single-molecule manipulation methods are useful techniques to probe the interactions of proteins and nucleic acid structures. Here, we describe magnetic tweezers-based single-molecule investigation of the binding of helicases to G-quadruplex structures and their ATP-dependent unwinding activity, using DHX36 (also known as RHAU and G4R1) helicase and both DNA and RNA G-quadruplex structures as examples. We specifically emphasize the principle and method to probe the interactions between DHX36 and the DNA G-quadruplex in different intermediate states during an ATPase cycle of DHX36, based on detecting the DHX36-induced changes in the lifetime of the DNA and RNA G-quadruplex under tension. The principle of the measurement can be broadly extended to the studies of other DNA or RNA G-quadruplex helicases.