Investigating fast dynamics at the tunneling ready state in formate dehydrogenase

Enzyme dynamics occur on a wide range of length and timescales. This work is focused on understanding enzyme dynamic at the fs-ps timescale as this is the dynamic range at which bonds are typically made and broken during chemical reactions. Our work focuses on enzymes that catalyze hydride transfer between two carbon atoms - a fundamental reaction in biology. Primary kinetic isotope effects and their temperature dependence have implied that fast dynamics of the enzyme are important in facilitating hydride transfer, however these experiments do not measure any such motions directly. We make use of two-dimensional infrared spectroscopy (2D IR), a technique that interrogates the vibrations of molecules to extract dynamic information from the surrounding environment with 100 fs resolution. A model system, formate dehydrogenase (FDH), is an excellent probe of dynamics at the fs-ps timescale. Azide bound to the ternary complex of FDH offers the ability to measure dynamics of an analog structure of the reactive complex using 2D IR, while also studying the reaction directly with and KIE’s and their temperature dependence. By altering various parts of the structure of FDH via mutagenesis and other techniques, we investigate the role of structure and dynamics to determine how fast dynamics of the active site influence the the kinetics of hydride transfer. These experiments are the first means of providing a dynamic interpretation of KIEs and their temperature dependence.