Substrate specificity for myelin basic protein-specific protein methylase I

Area of Science:

• Biochemistry
• Enzymology
• Protein Methylation

Background:

• Myelin basic protein (MBP) is a key component of myelin sheaths.
• Protein methylation, specifically of arginine residues, is a post-translational modification.
• MBP-specific protein methylase I (S-adenosyl-L-methionine:protein-L-arginine N-methyltransferase) catalyzes this modification.

Purpose of the Study:

• To investigate the substrate specificity of MBP-specific protein methylase I.
• To determine the minimal peptide length required for arginine methylation.
• To assess the methyl-accepting capacity of heterogeneous nuclear ribonucleoprotein (hnRNP) protein.

Main Methods:

• Comparative analysis of MBPs from different species as substrates.
• Synthesis and testing of various peptide fragments of bovine MBP.
• Assay of methyl-accepting properties of recombinant hnRNP protein.

Main Results:

• Carp MBP demonstrated the highest methyl acceptability among tested MBPs.
• A hexapeptide (Gly-Lys-Gly-Arg-Gly-Leu) was the shortest active methyl-accepting substrate, while a tetrapeptide was inactive.
• Methylarginine-deficient hnRNP protein was not methylated by MBP-specific or histone-specific protein methylase I.

Conclusions:

• Carp MBP's unique methylation status and sequence contribute to its high substrate acceptability.
• Specific sequence and length are critical for protein methylase I activity.
• The findings suggest the existence of a distinct protein methylase I specific for hnRNP proteins.