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Structural organization and developmental expression of the protein isoaspartyl methyltransferase gene from
M B O'Connor1, A Galus, M Hartenstine
1Department of Biology, Boston College, Chestnut Hill, MA 02167, USA.
Abstract:
A protein carboxyl methyltransferase activity (PCMT) with a specificity for age-damaged protein D-aspartyl and L-isoaspartyl residues (E.C. 2.1.1.77) has been identified and cloned in Drosophila. The Drosophila gene was localized by chromosome in-situ hybridization to region 83AB of the third chromosome. The methyltransferase coding sequence is distributed among four exons within a 1.4-kb segment of the genome; it predicts a polypeptide of 226 amino acids that is 55% identical to the mouse enzyme. When expressed in bacteria, the Drosophila protein exhibits PCMT activity. A single 1.4-kb Pcmt transcript is detected in RNA preparations from embryos, larvae, pupae and adults. The abundance of the transcript, which is lowest in larvae and highest in adults, parallels the specific activity of the enzyme measured in extracts from the same developmental stages. It has been proposed that the PCMT initiates the repair of structurally damaged cellular proteins. The constitutive expression of PCMT and the relatively high level of expression in postmitotic adult cells suggest that PCMT activity is required through development, but acquires additional significance in aging tissues.
Insights
Researchers identified and cloned a protein carboxyl methyltransferase (PCMT) in Drosophila, crucial for repairing age-damaged proteins. This enzyme
Area of Science:
- Biochemistry
- Molecular Biology
- Genetics
Background:
- Protein damage accumulates with age.
- Protein carboxyl methyltransferase (PCMT) repairs age-damaged proteins.
Purpose of the Study:
- To identify and characterize PCMT in Drosophila.
- To investigate the role of PCMT in protein repair and aging.
Main Methods:
- Gene cloning and sequencing in Drosophila.
- Chromosome in-situ hybridization for gene localization.
- Bacterial expression and enzyme activity assays.
Main Results:
- Drosophila PCMT gene cloned and localized to chromosome 3, region 83AB.
- Predicted 226-amino acid protein, 55% identical to mouse PCMT.
- Expressed Drosophila protein shows methyltransferase activity.
- PCMT transcript abundant in adults, lowest in larvae, correlating with enzyme activity.
- Constitutive expression suggests a role throughout development and aging.
Conclusions:
- Drosophila PCMT is involved in repairing age-damaged proteins.
- PCMT expression increases with age, highlighting its importance in aging tissues.
- This enzyme is essential for maintaining protein integrity during development and aging.