What Are the Common Post-Translational Modifications of Proteins? Provide Four Examples
Post-translational modifications (PTMs) are covalent modifications that occur after a protein has been synthesized from mRNA into a polypeptide chain. These modifications play a crucial role in determining protein function, activity, stability, and subcellular localization. The following are four representative types of post-translational modifications:
1. Phosphorylation
Phosphorylation is a pivotal post-translational modification that involves the covalent attachment of a phosphate group (PO₄³⁻) to specific amino acid residues, predominantly serine (Ser), threonine (Thr), or tyrosine (Tyr). This modification, catalyzed by protein kinases, is essential for cellular signaling pathways and protein function regulation.
2. Acetylation
Acetylation entails the addition of an acetyl group (-COCH₃) to lysine residues within a protein. This modification influences chromatin structure and gene transcription by altering protein-DNA and protein-protein interactions. A well-known example is histone acetylation, which plays a key role in gene expression regulation.
3. Glycosylation
Glycosylation refers to the enzymatic attachment of carbohydrate moieties to proteins, which significantly impacts their stability, folding, and functional roles in cell-cell recognition and signal transduction. This modification is particularly prevalent in secreted and membrane-associated proteins.
4. Ubiquitination
Ubiquitination is a regulatory post-translational modification characterized by the covalent conjugation of ubiquitin molecules to target proteins via a cascade of enzymatic reactions. This process primarily serves as a signal for proteasomal degradation, ensuring protein quality control and maintaining cellular proteostasis.
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