Methyl side-chain dynamics in proteins using selective enrichment with a single isotopomer

Area of Science:

• Biochemistry
• Structural Biology
• Chemical Synthesis

Background:

• 13C relaxation studies on protein side chains often use (13)CHD(2) isotopomers for simplified analysis.
• Current methods for obtaining these isotopomers in overexpressed proteins lead to mixed (2)H isotopomers, reducing data quality.

Purpose of the Study:

• To develop a chemical synthesis approach for pure (13)CHD(2) amino acid isotopomers.
• To overcome limitations in resolution and sensitivity in protein relaxation studies caused by mixed isotopomers.

Main Methods:

• Chemical synthesis of amino acids with a pure (13)CHD(2) isotopomer.
• 13C side-chain relaxation measurements on mouse major urinary protein selectively enriched with a synthesized valine isotopomer.
• Relaxation measurements in the presence and absence of pyrazine-derived ligands.

Main Results:

• Demonstrated a method to produce pure (13)CHD(2) isotopomers via chemical synthesis.
• Successfully applied this method to mouse major urinary protein, showing improved relaxation measurements.
• Valine side-chain dynamics were found to have minimal impact on ligand binding entropy.

Conclusions:

• The chemical synthesis of pure (13)CHD(2) isotopomers offers a significant advancement for protein dynamics studies.
• This technique enhances sensitivity and resolution, especially beneficial for larger protein systems.
• The findings suggest that valine side-chain flexibility is not a major driver of binding entropy in this system.