Efforts toward developing direct probes of protein dynamics

Area of Science:

• Biophysical Chemistry
• Protein Spectroscopy
• Vibrational Dynamics

Background:

• Infrared spectroscopy is a powerful tool for probing molecular vibrations.
• Understanding protein dynamics at the atomic level is crucial for deciphering biological function.
• Deuteration is a common technique to study vibrational properties in biomolecules.

Purpose of the Study:

• To perform the first infrared (IR) characterization of a single carbon-deuterium (C-D) bond within a protein.
• To investigate the vibrational behavior of deuterated methionine (Met80) in horse heart cytochrome c.
• To elucidate the factors influencing vibrational line shapes and energy relaxation in proteins.

Main Methods:

• Infrared (IR) spectroscopy was employed to analyze deuterated methionine (methyl-d1 and methyl-d3) within horse heart cytochrome c.
• Comparison of spectral line widths and line shapes between different deuteration patterns.
• Computational calculations of vibrational energy relaxation and Fermi resonance.

Main Results:

• The study achieved the first IR characterization of a single C-D bond in a protein.
• Methyl-d1 and asymmetric stretches of methyl-d3 showed inhomogeneous broadening.
• The symmetric stretch of methyl-d3 exhibited a significant homogeneous component.
• Vibrational energy relaxation calculations indicated stronger Fermi resonance for the symmetric stretch.

Conclusions:

• Observed differences in line width and line shape are attributed to variations in intramolecular vibrational relaxation (IVR).
• A stronger Fermi resonance in the symmetric stretch of methyl-d3 contributes to its distinct vibrational behavior.
• These findings provide new insights into the vibrational dynamics of C-D bonds within protein environments.