What Are Protein Post-Translational Modifications and Their Biological Functions
Post-translational modifications (PTMs) refer to chemical and functional alterations that occur in proteins following ribosomal synthesis. These modifications are mediated by the addition of chemical groups, cleavage of peptide bonds, conformational changes, or interactions with other biomolecules such as proteins, nucleic acids, or lipids. The major types of PTMs, along with their mechanisms of action and biological functions, are outlined below:
1. Phosphorylation
Phosphorylation involves the covalent attachment of phosphate groups to serine, threonine, or tyrosine residues by specific kinases. This modification functions as a key regulatory mechanism that alters protein activity or stability and modulates a wide array of signal transduction pathways.
2. Acetylation
Acetylation entails the transfer of acetyl groups to lysine residues of proteins, affecting protein–DNA interactions or protein–protein associations. It is particularly prominent in histone modification, where it plays a vital role in regulating gene expression.
3. Glycosylation
Glycosylation involves the enzymatic addition of glycan moieties to specific amino acid residues, impacting protein folding, structural stability, and cell–cell communication. This modification is essential for mediating cellular recognition and immune responses.
4. Ubiquitination
Ubiquitination is the process by which ubiquitin molecules are covalently attached to target proteins, commonly tagging them for degradation via the proteasome pathway or modulating signaling pathways. It is crucial for maintaining protein homeostasis and regulating the cell cycle.
5. Methylation
Methylation involves the addition of methyl groups to selected amino acid residues, often lysine or arginine. This modification can influence protein–DNA binding affinity or enzymatic activity and plays a significant role in epigenetic regulation.
These post-translational modifications are indispensable for normal cellular operations. By regulating protein activity, localization, interactions, and stability, PTMs govern numerous fundamental biological processes, including signal transduction, gene expression, and cell division.
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