Extracting the Hydrolysis Rate Constant from a Single-Molecule Controlled Rotation Experimental Data on a F1-ATPase

Abstract

The chemo-mechanical energy transduction of the ATP Synthase is at the heart of the biological function, and it can be elucidated by studying the water soluble F1-ATPase, focusing on the individual sub-steps of the reactions in the enzyme. In controlled rotation experiment single F1-ATPase molecules deposited on a microscope slide are rotated by magnetic tweezers. Simultaneously the individual ATP binding and ADP release events are monitored by single molecule fluorescence imaging in real time. Our goal is to extract the ATP hydrolysis and synthesis rate constants as a function of rotor angle from the single molecule binding and release data. This work requires advanced analysis because these processes occurring in the binding pocket are “hidden”, and not directly monitored. Our approach is based on the treatment of composite events developed by Volkan-Kacso and Marcus, for a constant rotation rate. We will use high-quality single-molecule trajectories provided by our experimentalist collaborator K. Adachi, who pioneered the method of controlled rotation. Preliminary results indicate that fluorescent Cy3-ATP hydrolyses about 100 times slower than the wild species (ATP), at rotor angle of 240 degrees, its rate is about 1.7 X 10⁻³ per seconds. We plan to extract the hidden hydrolysis and synthesis rates for the complete 360 degrees cycle.