Ultrafast conformational changes in carbonmonoxy-myoglobin after photolysis observed by time-resolved circular dichroism

An understanding of the first steps of conformational changes in proteins is very challenging. In that prospect, the processes occurring in carboxymyoglobin (MbCO) after ligand dissociation have been thoroughly studied. However, time-resolved absorption or Raman experiments, which probe localized electronic or vibrational modes of the protein, do not provide much information on the global conformation changes. Such is not the case for circular dichoism (CD), which is very sensitive to the geometry of the whole molecule. This chapter presents a subpicosecond time-resolved CD experiment on photolyzed MbCO and couples it with a CD calculation based on the polarizability theory to access information on the geometrical relaxation of the protein. Conformational changes are observed on a sub-100 ps timescale that is assigned to the strain brought onto the proximal histidine by the heme doming.