Myoglobin's ultrafast dynamics measured with vibrational echo experiments

Abstract

Ultrafast infrared (IR) vibrational echo experiments, which are used to examine the ultrafast dynamics of myoglobin and myoglobin mutants are described. Like the NMR spin echo and other NMR pulse sequences, the vibrational echo can extract dynamical and spectroscopic information that cannot be obtained from a vibrational absorption spectrum. The vibrational echo measures the homogenous vibrational linewidth even if the absorption line is massively inhomogeneously broadened. When combined with pump-probe (transient absorption) experiments, the homogeneous pure dephasing (energy level fluctuations) is obtained. Conducting these experiments as a function of temperature provides information on dynamics and intermolecular interactions. The nature of the method and the experimental procedures are outlined. The dynamics of the CO ligand bound at the active site of the protein myoglobin are examined and compared with that in myoglobin mutants. The results provide insights into protein dynamics and how protein structural fluctuations are communicated to a ligand bound at the active site.