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Specific recognition of altered polypeptides by widely distributed methyltransferases
Biochemical and Biophysical Research Communications
|November 15, 1985
Summary
Protein carboxyl methyltransferase activity, crucial for cellular function, was found in bacteria, amphibian oocytes, and mammalian cells. This enzyme specifically methylates atypical aspartyl residues, indicating a vital role in protein repair.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Protein damage and aging can lead to the accumulation of atypical amino acid residues, such as isoaspartate.
- Enzymatic repair mechanisms are essential for maintaining protein integrity and cellular function.
- Protein carboxyl methyltransferases (PCMTs) are enzymes involved in protein repair through methylation.
Purpose of the Study:
- To investigate the presence and substrate specificity of protein carboxyl methyltransferase activity in various organisms.
- To determine if this activity recognizes and methylates atypical aspartyl residues in proteins.
- To understand the potential significance of this enzymatic activity in different cell types.
Main Methods:
- Extraction of enzymatic activity from bacterial (Salmonella typhimurium) cells, Xenopus laevis oocytes, and mammalian cell lines.
- Assaying methyltransferase activity using synthetic peptides containing either normal L-aspartyl or L-isoaspartyl residues.
- Comparing the substrate preference of the identified activities with known PCMTs from human erythrocytes and bovine brain.
Main Results:
- Protein carboxyl methyltransferase activity was detected in bacterial, amphibian, and mammalian cell extracts.
- The enzyme activity specifically recognized and methylated a synthetic peptide containing an L-isoaspartyl residue, but not one with a normal L-aspartyl residue.
- The observed enzymatic activities were comparable to previously characterized PCMTs involved in methyl ester formation of atypical aspartyl residues.
Conclusions:
- The widespread presence of protein carboxyl methyltransferase activity across diverse species suggests a fundamental cellular role.
- This enzyme's specific recognition of atypical aspartyl residues highlights its importance in protein repair and maintenance.
- The methylation of aberrant proteins is likely an essential function for cellular health and longevity.