Direct observation of ultrafast collective motions in CO myoglobin upon ligand dissociation

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Science  10 Sep 2015:
DOI: 10.1126/science.aac5492

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The hemoprotein myoglobin is a model system to study protein dynamics. We used time-resolved serial femtosecond crystallography at an x-ray free-electron laser to resolve the ultrafast structural changes taking place in the carbonmonoxy myoglobin complex upon photolysis of the Fe-CO bond. Structural changes appear throughout the protein within 500 fs with the C-, F- and H-helices moving away from the heme and the E- and A-helices moving toward it. These collective movements are predicted by quantum mechanics/molecular mechanics simulations. Together with the observed oscillations of residues contacting the heme, the calculations support predictions that an immediate collective response of the protein takes place upon ligand dissociation due to coupling of vibrational modes of the heme to global modes of the protein.

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