Speaker
Dr
Camila Bacellar
(PSI)
Description
Iron-containing heme proteins are amongst the most important known proteins and the metal-binding center is paramount to the function of these systems. Much effort has been dedicated to the study of the structure, function and dynamics of these proteins. Time-resolved X-ray spectroscopy is a particularly well-suited tool for this purpose given that the element specificity provides a direct and sensitive probe of the dynamics from the metal-binding center point of view. This work focuses in the investigation of light-induced ultrafast electronic and structural dynamics of two important heme proteins, Nitrosyl Myoglobin (MbNO) and Cytochrome C (CytC), by time-resolved x-ray absorption (XAS) and x-ray emission (XES) spectroscopies.
Upon visible photoexcitation of the heme group, MbNO undergoes dissociation of the ligand which is accompanied by a spin change and a structural reconfiguration of the porphyrin ring. Part of the excited population undergoes recombination in multiple timescales through an intermediate state that is presumed to be a high spin domed ligated form of MbNO. We carried out a time-resolved XES experiment and the results offer new insight on the dissociation-recombination dynamics and capture all the intermediate spin states involved in the relaxation from the initially excited heme back to the ground state.
Meanwhile, CytC we focused on the investigation of the nature of the relaxation process fowling excitation of the heme in its ferric form. Ferrous heme proteins (such as the MbNO) are known for undergoing dissociation of the axial ligand, however, this is not observed in their ferric counterparts. This has led to a long discussion of the relaxation pathway involved in these types of systems, which was believed to proceed entirely via vibrational cooling back to the ground state. We recently performed fs-XAS and fs-XES experiments that challenge this interpretation evidencing the presence of heme doming and de-excitation via high spin states.
Primary author
Dr
Camila Bacellar
(PSI)
