Cryogenic stabilization of myoglobin photoproducts

Area of Science:

• Biophysics
• Spectroscopy
• Protein Dynamics

Background:

• Myoglobin and hemoglobin are crucial oxygen-binding proteins.
• Understanding their structural dynamics is key to their function.
• Carbon monoxymyoglobin serves as a model for photodissociated states.

Purpose of the Study:

• To investigate the low-frequency resonance Raman spectra of photodissociated carbon monoxymyoglobin.
• To compare these spectra with those of deoxymyoglobin at cryogenic temperatures.
• To elucidate the structural and dynamic differences between these states.

Main Methods:

• Low-frequency resonance Raman spectroscopy.
• Cryogenic temperature studies (4-77 K).
• Comparison of spectral features (frequency, intensity) of porphyrin and iron-histidine modes.

Main Results:

• Significant differences in low-frequency porphyrin modes between photodissociated and deoxymyoglobin.
• Distinct changes in the iron-histidine stretching mode (frequency and intensity) in the photoproduct.
• Temperature-dependent intensity changes in the iron-histidine mode of the photoproduct.
• Differences persisted across different buffer conditions and temperatures up to 77 K.

Conclusions:

• The tilt angle of histidine and orbital overlap govern the iron-histidine mode's frequency and intensity.
• This model explains spectral differences in both myoglobin and hemoglobin photoproducts.
• Low-temperature relaxation pathways for hemoglobin and myoglobin are proposed based on these findings.