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Selective methyl esterification of erythrocyte membrane proteins by protein methylase II
Abstract:
Methyl esterification of erythrocyte membrane proteins have been demonstrated by incubating the isolated membrane with purified protein methylase II (S-adenosyl-methionine:protein-carboxyl O-methyltransferase, EC 2.1.1.24) and S-adenosyl-L-[methyl-14C]methionine. Methyl esterification of membrane-bound proteins occurred selectively to proteins corresponding to bands 3 (mol wt 97 000), 4 (mol wt 75 000), and 4.5 (mol wt 48 000) [designated according to Steck, T. L. (1974), J. Cell Biol. 62, 1] as identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Mild alkali treated depleted vesicles which lacked bands 1, 2, 5, and 6 had a higher methyl accepting capacity; 500 pmol of methyl groups/mg of depleted vesicle proteins vs. 200 pmol of methyl groups/mg of intact membrane proteins. Alkali-extractable membrane components were not methylated.
Insights
Erythrocyte membrane proteins undergo methyl esterification, primarily targeting specific proteins like band 3. This process, mediated by protein methylase II, shows increased capacity in alkali-treated vesicles lacking certain membrane components.
Area of Science:
- Biochemistry
- Cell Biology
- Membrane Protein Research
Background:
- Erythrocyte membranes contain numerous proteins involved in cellular functions.
- Protein methylation is a post-translational modification with diverse biological roles.
Purpose of the Study:
- To investigate the methyl esterification of erythrocyte membrane proteins.
- To identify specific membrane proteins susceptible to methylation by protein methylase II.
Main Methods:
- Incubation of isolated erythrocyte membranes with purified protein methylase II and radiolabeled S-adenosyl-L-methionine.
- Analysis of protein methylation patterns using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).
- Comparison of methyl-accepting capacity in intact versus alkali-treated erythrocyte vesicles.
Main Results:
- Selective methyl esterification of erythrocyte membrane proteins, specifically bands 3, 4, and 4.5.
- Identified proteins correspond to specific molecular weights (97,000, 75,000, and 48,000 Da).
- Alkali-treated vesicles, depleted of certain proteins, exhibited a significantly higher methyl-accepting capacity (500 pmol/mg) compared to intact membranes (200 pmol/mg).
Conclusions:
- Protein methylase II specifically methylates certain erythrocyte membrane proteins.
- The methyl-accepting capacity of erythrocyte membranes is influenced by the presence or absence of specific protein components.
- Alkali-extractable membrane components are not substrates for this methylation reaction.