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Widespread phylogenetic distribution of a protein methyltransferase that modifies L-isoaspartyl residues
B A Johnson1, S Q Ngo, D W Aswad
1School of Biological Sciences, University of California, Irvine 92717.
Abstract:
Protein L-isoaspartyl methyltransferase is implicated in the repair or degradation of age-damaged proteins that contain atypical, L-isoaspartyl residues. The enzyme has previously been demonstrated in a variety of vertebrates and in the bacterium S. typhimurium (O'Connor, C.M. and Clarke, S. (1985) Biochem. Biophys. Res. Commun. 132, 1144-1150). We report here that the enzyme is present in a mollusc (great slug), a crustacean (pill woodlouse), a fungus (mushroom), and a plant (wheat germ). Using mushroom as an example, we show that the enzyme activity may, in some instances, require a partial purification before its presence is clearly detectable. Our findings significantly extend the known phylogenetic distribution of this enzyme and suggest that it may play an indispensable role in protein metabolism.
Insights
Protein L-isoaspartyl methyltransferase, an enzyme repairing damaged proteins, was found in diverse organisms like molluscs, crustaceans, fungi, and plants. This discovery broadens its known phylogenetic distribution, suggesting a vital role in protein metabolism.
Area of Science:
- Biochemistry
- Molecular Biology
- Evolutionary Biology
Background:
- Protein damage accumulates with age, containing atypical L-isoaspartyl residues.
- Protein L-isoaspartyl methyltransferase (PIMT) repairs these age-damaged proteins.
- PIMT has been identified in vertebrates and bacteria.
Purpose of the Study:
- To investigate the presence and phylogenetic distribution of PIMT in non-vertebrate and non-bacterial organisms.
- To explore the potential role of PIMT in broader protein metabolism.
Main Methods:
- Enzyme assays were performed on extracts from various organisms.
- Partial purification techniques were employed for enzyme activity detection, using mushroom as a model.
- Phylogenetic analysis of PIMT distribution was conducted.
Main Results:
- PIMT activity was detected in a mollusc (great slug), a crustacean (pill woodlouse), a fungus (mushroom), and a plant (wheat germ).
- Enzyme activity in mushroom required partial purification for clear detection.
- The findings significantly extend the known evolutionary range of PIMT.
Conclusions:
- PIMT is widely distributed across diverse eukaryotic kingdoms, including invertebrates and plants.
- The enzyme's presence suggests a fundamental and indispensable role in protein maintenance and metabolism.
- Further research is warranted to elucidate PIMT's specific functions in these diverse organisms.