Homocysteine Thiolactone Modification of Ribonuclease A: Thermodynamics and Kinetics
Kabira Sabnam1, Swagata Dasgupta1
1Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur, India.
Proteins
|April 4, 2025
Summary
Homocysteine thiolactone modifies proteins like Ribonuclease A (RNase A), forming dimers and reducing enzyme activity. This study reveals structural changes and functional impairment in modified RNase A, offering insights into disease mechanisms.
Area of Science:
- Biochemistry
- Molecular Biology
- Proteomics
Background:
- Elevated homocysteine thiolactone levels are linked to various human diseases.
- N-homocysteinylation modifies lysine residues in proteins, potentially leading to dimerization and oligomerization.
- Understanding protein modifications is crucial for deciphering disease pathologies.
Purpose of the Study:
- To investigate the structural and functional effects of N-homocysteinylation on Ribonuclease A (RNase A).
- To elucidate how homocysteine thiolactone modification impacts RNase A's activity and integrity.
- To contribute to understanding hyperhomocysteinemia-related pathologies.
Main Methods:
- Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Matrix-Assisted Laser Desorption/Ionization-Time of Flight (MALDI-ToF) mass spectrometry to confirm protein oligomerization.
- Agarose-gel assays to assess ribonucleolytic activity.
- Fluorescence spectroscopy to probe changes in the tyrosine microenvironment.
- Circular Dichroism (CD) melting studies to analyze secondary structure alterations.
- Isothermal Titration Calorimetry (ITC) and UV-visible kinetics to quantify enzyme activity.
Main Results:
- N-homocysteinylation of RNase A leads to the formation of dimers and higher-order oligomers.
- Modified RNase A exhibits reduced ribonucleolytic activity.
- Spectroscopic and CD analyses indicate local structural changes, including altered secondary structure content (enhanced β-sheet, reduced α-helix), but overall structural integrity is maintained.
- ITC and kinetic studies confirm a significant decrease in enzyme activity upon homocysteinylation.
Conclusions:
- N-homocysteinylation induces significant structural and functional alterations in RNase A.
- The observed changes in RNase A provide a molecular basis for understanding the impact of hyperhomocysteinemia on protein function.
- This study enhances our comprehension of how homocysteine thiolactone contributes to disease pathogenesis.
Keywords:
dimer formationkinetic parametersribonuclease Aribonucleolytic activitythermodynamic parametersMore Related Videos
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