Probing protein structure and dynamics with resonance Raman spectroscopy: cytochrome c peroxidase and hemoglobin.
Because vibrational frequencies are sensitive to structure, RR spectroscopy can provide structural information about kinetic steps in protein transformations when carried out in a time-resolved mode. UVRR spectroscopy has shown that the aromatic groups of the HbCO photoproduct respond with a delay of 20 microseconds and has provided direct structural evidence that the 20-microseconds kinetic step is the R-T quaternary re-arrangement of the subunits. RR bands of the porphyrin ring show that the core relaxes via a 0.1-microsecond protein motion, which probably allows the Fe atom to attain its full out-of plane displacement. The Fe-His stretching frequency has an elevated value immediately after CO photolysis, in part, perhaps, because of the protein constraint on the Fe displacement. It relaxes on both the 0.1- and 1-microsecond time scales to its value in R-state Hb and then decreases further to its T-state value. These changes may be connected with reorientation of the proximal His side chain. At very early times after a photolysis pulse, heating effects may be an important aspect of the protein dynamics, but further experiments are needed to understand the RR response.
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Department of Chemistry, Princeton University, New Jersey 08562.
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D000495:Allosteric Site; D003578:Cytochrome-c Peroxidase; D006454:Hemoglobins; D006860:Hydrogen Bonding; D015394:Molecular Structure; D010544:Peroxidases; D011487:Protein Conformation; D013059:Spectrum Analysis, Raman
D006454:Hemoglobins; D010544:Peroxidases; D003578:Cytochrome-c Peroxidase