Direct Measurement of Single-Molecule Adenosine Triphosphatase Hydrolysis Dynamics

F₁-ATPase (F₁) is a bidirectional molecular motor that hydrolyzes nearly all ATPs to fuel the cellular processes. Optical observation of labeled F₁ rotation against the α₃β₃ hexamer ring revealed the sequential mechanical rotation steps corresponding to ATP binding/ADP release and ATP hydrolysis/Pi release. These substeps originate from the F₁ rotation but with heavy load on the γ shaft due to fluorescent labeling and the photophysical limitation of an optical microscope, which hampers better understanding of the intrinsic kinetic behavior of ATP hydrolysis. In this work, we present a method capable of electrically monitoring ATP hydrolysis of a single label-free F₁ in real time by using a high-gain silicon nanowire-based field-effect transistor circuit. We reproducibly observe the regular current signal fluctuations with two distinct levels, which are induced by the binding dwell and the catalytic dwell, respectively, in both concentration- and temperature-dependent experiments. In comparison with labeled F₁, the hydrolysis rate of nonlabeled F₁ used in this study is 1 order of magnitude faster (1.69 × 10⁸ M^-1 s^-1 at 20 °C), and the differences between two sequential catalytic rates are clearer, demonstrating the ability of nanowire nanocircuits to directly probe the intrinsic dynamic processes of the biological activities with single-molecule/single-event sensitivity. This approach is complementary to traditional optical methods, offering endless opportunities to unravel molecular mechanisms of a variety of dynamic biosystems under realistic physiological conditions.