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Post-translational modification (PTM) can be defined as the change in the chemical structure of a protein after it is completely formed. This is a covalent process that takes place by total wage, by addition of new chemical groups, or by modifying the existing groups like methyl, phosphoryl, acetyl, etc. Post-translational modification can be reversible or irreversible. The reversible reactions of the post-translational modification have covalent modifications, and reversible reactions have proteolytic modifications. The post-translational modification affects a single type of a minor acid or multiple amino acids, leading to a change in the chemical property of the modified amino acid. Post-translational modifications help in protein biosynthesis because proteins are continuously degraded and formed by post-translational modifications into functional proteins.
The significance of post-translational modifications
Post-translational modifications are seen in important structural and functional proteins like membrane protein, histone protein, and secretary protein. These post-transitional changes affect a broad spectrum of characteristics of the protein, which include protein solubility, protein folding, protein interaction, protein lifespan, and protein localization. In a general lookout, the post-translational modification affects certain biological processes, including control of cell cycle activation of gene DNA repair, gene expression and regulation transaction, and control over the cell cycle.
To study post-translational modification, we use an immunoassay technology called proximity ligation assay, abbreviated as “PLA”. Besides proximity ligation assay, we have immunoprecipitation (IP) to detect different PTM assays. Combining IP with mass spectrometry is an effective method of detecting PTM.
Types of post-translational modification
We shall discuss the different types of PTM, including acetylation and methylation, which are based on the addition of chemical compounds.
Acetylation: Acetylation can be defined as modification by adding an acetyl group. The acetyl modification was first discovered by VG Alfrey in 1964 in an isolated calf thymus nuclei. Acetylation is involved in several biological processes and functions like protein stability, protein synthesis, DNA stability, and cancer. Acetylation is catalysed by lysine acetyltransferase and histone acetyltransferase enzymes. Acetylation of the histone protein reduces its positive charge and, thereby, its interaction with negatively charged phosphate groups of the DNA. Acetylation and deacetylation of histone protein are major parts of gene regulation. Acetyltransferase uses the cofactor acetyl CoA to add the acetyl group, whereas deacetylation removes an acetyl group on the lysine side chain. Three forms of acetylation can be observed in the process. According to a report, acetylated lysine is helpful for self cell development, and its functioning can lead to serious diseases like neurological disease, immune disorder, cancer, and cardiovascular diseases. Acetylation of p53, a tumour-suppressing gene, is crucial for it to function properly and express its growth-suppressing property. Protein acetylation can be discovered in many ways, including chromatin immunoprecipitation by the use of acetyl lysine-specific antibodies and also by the use of mass spectroscopy. An increase in the weight of histone protein by 42 mass units represents a single acetylation reaction.
Methylation: Research on methylation has been conducted since 1939. We have recently discovered New methyltransferase enzymes and histone lysine methyltransferase. Methylation is a reversible post-translational modification that is reversible in nature and occurs more often in the nucleus and the nuclear proteins involving histone protein. Methylation is the addition of a methyl group to the lysine or arginine residue of a protein. Arginine can be methylated once or twice, whereas lysine can be methylated once, twice, or thrice. Enzymes like methyltransferase help in the process of methylation. In eukaryotes, methylated arginine has been observed in histone and non-histone proteins. In histone, protein methylation can lead to gene repression or gene activation. Methylation is associated with many biological processes, including transcriptional regulation to epigenetic silencing. Defects in methylation can lead to diseases like diabetes mellitus, mental retardation, and cancer.
Conclusion
Hence, it can be concluded that post-translational modification in protein is a necessary process that takes place after the protein is completely formed. Post-translational modifications help convert proteins into functional proteins to perform various functions like controlling cell cycle gene expression, gene repression, etc. We defined post-translational modifications into two types: acetylation and methylation. While acetylation is the addition of the acetyl group, methylation is the addition of the methyl group. Defects in acetylation and methylation can cause serious diseases like cancer, diabetes mellitus, and mental retardation.
