Observing heme doming in myoglobin with femtosecond X-ray absorption spectroscopy

Abstract

We report time-resolved X-ray absorption measurements after photolysis of carbonmonoxy myoglobin performed at the LCLS X-ray free electron laser with nearly 100 fs (FWHM) time resolution. Data at the Fe K-edge reveal that the photoinduced structural changes at the heme occur in two steps, with a faster (∼70 fs) relaxation preceding a slower (∼400 fs) one. We tentatively attribute the first relaxation to a structural rearrangement induced by photolysis involving essentially only the heme chromophore and the second relaxation to a residual Fe motion out of the heme plane that is coupled to the displacement of myoglobin F-helix.

Perspective: Opportunities for ultrafast science at SwissFEL

“…The latter studies repeated those by Santomauro et al 125 using the slicing scheme, but this time with a greatly enhanced S/N, which allowed them to detect a factor of 3 between the electron trapping time (∼100 fs) and the ensuing structural relaxation of the trap (∼300 fs). Finally, following the fs Fe K-edge XAS experiment on Carboxymyoglobin (MbCO) at single probe energies, 132 polarized fs Co K-edge XANES on Vitamin B12 was for the first time reported, probing the structural evolution of the protein 141 . In another study, Mara and co-workers reported an ultrafast energy-resolved XAS and XES study of photoexcited ferrous Cytochrome C 142 .…”

Activation of coherent lattice phonon following ultrafast molecular spin-state photo-switching: A molecule-to-lattice energy transfer

“…Such transformations, as well as their recovery towards the stable state, involve not only the photoactive center with a molecular transformation but also its environment (Schoenlein et al , 1991; Elsaesser and Kaiser, 1991; Barbara et al , 1992; Rosspeintner et al , 2013; Jun et al , 2015; and Levantino et al , 2015a; 2015b). For example, the energy transfer between a “hot” photo-excited molecule and its surrounding solvent is at the origin of molecular vibrational cooling and solvent heating.…”

Time-resolved X-ray spectroscopies of chemical systems: New perspectives

“…In a recent study, Collet and co-workers reported fs XANES studies of a molecular crystals consisting of SCO molecules 84 . In another study, Levantino et al 80 . reported the first fs XAS experiment on a protein, Carboxymyoglobin (MbCO).…”