Ribonuclease S dynamics measured using a nitrile label with 2D IR vibrational echo spectroscopy

Area of Science:

• Biophysics
• Protein Dynamics
• Spectroscopy

Background:

• Ribonuclease S is a semisynthetic enzyme crucial for RNA processing.
• Understanding protein dynamics is key to enzyme function and mechanism.
• Nitrile-labeled amino acids offer a sensitive probe for molecular motion.

Purpose of the Study:

• To investigate the protein dynamics of ribonuclease S using a nitrile-labeled amino acid.
• To compare the dynamics of the S-peptide and the intact ribonuclease S complex.
• To validate molecular dynamics simulations against experimental data for protein fluctuations.

Main Methods:

• Two-dimensional infrared (2D IR) vibrational echo spectroscopy on nitrile-labeled S-peptide and ribonuclease S.
• Analysis of line shape changes using the center line slope method to obtain the frequency-frequency correlation function (FFCF).
• Molecular dynamics (MD) simulations to model equilibrium dynamics and compare with experimental FFCFs.

Main Results:

• The nitrile probe in the S-peptide exhibits dynamics faster than free p-cyanophenylalanine in water.
• In the ribonuclease S complex, nitrile probe dynamics are dominated by homogeneous dephasing, with minimal inhomogeneous contributions.
• MD simulations provide comparable FFCFs, supporting their ability to capture fast protein dynamics.

Conclusions:

• The study elucidates the distinct dynamic behaviors of the S-peptide and the ribonuclease S complex.
• Nitrile labeling provides valuable insights into protein structural fluctuations at fast time scales.
• The findings validate the use of MD simulations for studying protein dynamics under thermal equilibrium.