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Methyl-esterified proteins in a mammalian cell line
Biochemistry
|November 5, 1985
Summary
Methyl esterification modifies over 24 proteins in mouse lymphoma cells, with distinct proteins found in cellular fractions. This process, unlike phosphorylation, occurs at a lower steady-state level.
Area of Science:
- Biochemistry
- Cell Biology
- Proteomics
Background:
- Protein modification is crucial for cellular function.
- Methyl esterification of proteins is a less-studied post-translational modification compared to phosphorylation.
- Understanding protein methylation in lymphoma cells provides insights into cellular regulation.
Purpose of the Study:
- To investigate methyl esterification of carboxylic acid residues in intact mouse S49 lymphoma cells.
- To identify and localize methyl-esterified proteins within cellular compartments.
- To determine the turnover rate and stability of methyl-esterified proteins.
Main Methods:
- Cell fractionation to isolate nuclei, plasma membrane/mitochondria, microsomes, and soluble fractions.
- Incubation of cell homogenates with S-adenosyl-L-[methyl-3H]methionine to identify methyl-esterified proteins.
- Pulse-chase experiments to determine protein demethylation half-lives.
- Assessment of methyl group incorporation under conditions of blocked protein synthesis.
Main Results:
- At least 24 proteins were found to be methyl esterified.
- Specific sets of methyl-esterified proteins were localized to nuclei (11 proteins), plasma membrane/mitochondria (5 proteins), microsomes (2 proteins), and soluble fractions (6 proteins).
- Methyl group incorporation into protein occurred at approximately 118 pmol/mg protein, significantly lower than phosphorylation.
- Methyl-esterified proteins exhibited demethylation half-lives between 2.6 and 9.3 hours.
- Methyl group incorporation into protein was relatively resistant to the inhibition of protein synthesis.
Conclusions:
- Methyl esterification is a widespread protein modification in mouse lymphoma cells, with distinct subcellular localization.
- The turnover of methyl groups on proteins is dynamic, with measurable demethylation rates.
- Methyl esterification represents a distinct regulatory mechanism compared to phosphorylation, with different incorporation levels and turnover dynamics.