Related Experiment Videos
Myelin basic protein inhibits histone-specific protein methylase I
Abstract:
Bovine brain myelin basic protein, free of associated proteolytic activity, was found to be a specific inhibitor of histone-specific protein methylase I (S-adenosyl-L-methionine:protein-L-arginine N-methyltransferase, EC 2.1.1.23) purified from bovine brain. 50% of the methyl group incorporation into the histone substrate catalyzed by the methylase I was inhibited by myelin basic protein at a concentration of 0.326 mM. However, neither of the peptide fragments (residues 1-116 and residues 117-170) generated by the chemical cleavage of myelin basic protein at the tryptophan residue retained the inhibitory activity for histone-specific protein methylase I. Proteins such as gamma-globulin, bovine serum albumin, bovine pancreatic ribonuclease and polyarginine did not exhibit significant inhibitory activity toward the enzyme. The Ki value for myelin basic protein was estimated to be 3.42 X 10(-5) M for histone-specific protein methylase I and the nature of the inhibition was uncompetitive toward histone substrate.
Insights
Bovine brain myelin basic protein specifically inhibits histone-specific protein methylase I. This inhibitory activity is lost in its peptide fragments, indicating the full protein structure is crucial for inhibition.
Area of Science:
- Biochemistry
- Neuroscience
- Enzymology
Background:
- Histone methylation plays a critical role in gene regulation.
- Protein methyltransferases are key enzymes in this process.
- Understanding enzyme inhibitors aids in dissecting cellular pathways.
Purpose of the Study:
- To identify specific inhibitors of histone-specific protein methylase I.
- To investigate the inhibitory potential of bovine brain myelin basic protein (MBP).
- To characterize the mechanism of inhibition by MBP.
Main Methods:
- Purification of histone-specific protein methylase I from bovine brain.
- Assay of methylase activity using histone substrate and S-adenosyl-L-methionine.
- Chemical cleavage of MBP and testing of peptide fragments for inhibitory activity.
- Enzyme kinetics to determine inhibition constant (Ki) and mechanism.
Main Results:
- Bovine brain MBP specifically inhibited histone-specific protein methylase I.
- MBP inhibited 50% of methyl group incorporation at 0.326 mM.
- Neither MBP peptide fragment (1-116 or 117-170) retained inhibitory activity.
- Other proteins like gamma-globulin and BSA showed no significant inhibition.
- The Ki for MBP was 3.42 X 10(-5) M, with uncompetitive inhibition toward the histone substrate.
Conclusions:
- Bovine brain MBP is a specific inhibitor of histone-specific protein methylase I.
- The full structure of MBP is essential for its inhibitory function.
- MBP's uncompetitive inhibition suggests a regulatory role in histone methylation pathways.