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Methyl acceptors for protein methylase II from human-erythrocyte membrane
Abstract:
Membrane proteins from human erythrocytes were methylated with purified protein methylase II (S-adenosylmethionine:protein-carboxyl O-methyltransferase, EC.2.1.1.24). The methylated proteins were analyzed by dodecyl sulfate/polyacrylamide gel electrophoresis. Monomeric and dimeric glycophorin A (NaIO4/Schiff-2 and NaIO4/Schiff-1 positive bands) and 'band 4.5' were identified as two major classes of methyl-acceptor polypeptides for protein methylase II. In rabbit erythrocyte membrane where glycophorin A is absent, 'band 4.5' was the only major methyl-acceptor protein component. Extracted and purified glycophorin A from human erythrocytes was also found to be an excellent substrate for protein methylase II with a Km of 35.7 microM. The role of erythrocyte membrane protein methylation is discussed with regard to membrane function.
Insights
Human erythrocyte membrane proteins, including glycophorin A, undergo methylation by protein methylase II. This process modifies key membrane proteins, potentially impacting erythrocyte function.
Area of Science:
- Biochemistry
- Cell Biology
- Membrane Protein Research
Background:
- Erythrocyte membrane proteins play crucial roles in cell structure and function.
- Protein methylation is a post-translational modification that can alter protein properties and interactions.
- Understanding protein methylation in erythrocytes provides insights into cellular processes.
Purpose of the Study:
- To identify the specific erythrocyte membrane proteins that serve as substrates for protein methylase II.
- To investigate the role of glycophorin A in protein methylation within human erythrocytes.
- To compare protein methylation patterns between human and rabbit erythrocytes.
Main Methods:
- Methylation of human erythrocyte membrane proteins using purified protein methylase II.
- Analysis of methylated proteins via dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE).
- Extraction and purification of glycophorin A for substrate analysis.
Main Results:
- Glycophorin A (monomeric and dimeric forms) and 'band 4.5' were identified as major methyl-acceptor polypeptides in human erythrocytes.
- 'Band 4.5' was the sole major methyl-acceptor protein in rabbit erythrocytes, which lack glycophorin A.
- Purified glycophorin A demonstrated to be an excellent substrate for protein methylase II, with a Km of 35.7 μM.
Conclusions:
- Protein methylase II specifically methylates glycophorin A and 'band 4.5' in human erythrocyte membranes.
- The absence of glycophorin A in rabbit erythrocytes results in 'band 4.5' being the primary methylation target.
- Erythrocyte membrane protein methylation, particularly of glycophorin A, likely plays a significant role in membrane function.