Posttranslational Modifications to Know for Biological Chemistry II

Posttranslational modifications are essential chemical changes that proteins undergo after translation. These modifications, like phosphorylation and glycosylation, fine-tune protein function, stability, and interactions, playing a vital role in cellular processes and signaling pathways within Biological Chemistry II.

1. Phosphorylation

   • Involves the addition of a phosphate group, typically to serine, threonine, or tyrosine residues.
   • Regulates protein function, activity, and interactions, often acting as a molecular switch.
   • Mediated by kinases (add phosphate) and phosphatases (remove phosphate), playing a crucial role in signal transduction pathways.

2. Glycosylation

   • The attachment of carbohydrate moieties to proteins, influencing stability, localization, and function.
   • Two main types: N-linked (to asparagine) and O-linked (to serine or threonine).
   • Critical for cell-cell recognition, immune response, and protein folding.

3. Ubiquitination

   • The process of attaching ubiquitin, a small protein, to lysine residues on target proteins.
   • Primarily signals for protein degradation via the proteasome, regulating protein turnover.
   • Also involved in DNA repair, cell cycle regulation, and immune responses.

4. Methylation

   • The addition of methyl groups, usually to lysine or arginine residues in histones and other proteins.
   • Plays a key role in gene regulation, influencing chromatin structure and transcriptional activity.
   • Can either activate or repress gene expression depending on the context.

5. Acetylation

   • Involves the addition of acetyl groups to lysine residues, affecting protein stability and function.
   • Commonly associated with histone modification, leading to changes in gene expression.
   • Can also regulate non-histone proteins, impacting various cellular processes.

6. SUMOylation

   • The attachment of Small Ubiquitin-like Modifier (SUMO) proteins to target proteins.
   • Modulates protein stability, localization, and activity, often influencing transcriptional regulation.
   • Plays a role in stress response, DNA repair, and cell cycle control.

7. Proteolytic cleavage

   • The enzymatic cleavage of peptide bonds in proteins, leading to activation or inactivation of protein function.
   • Commonly seen in the activation of zymogens (inactive precursors) into active enzymes.
   • Important for regulating signaling pathways and protein turnover.

8. Disulfide bond formation

   • The formation of covalent bonds between cysteine residues, stabilizing protein structure.
   • Crucial for the proper folding and stability of extracellular proteins.
   • Plays a significant role in the function of antibodies and secreted proteins.

9. Lipidation

   • The addition of lipid groups to proteins, which can affect membrane localization and protein-protein interactions.
   • Common types include myristoylation and palmitoylation, influencing signaling pathways.
   • Important for the function of many signaling proteins and membrane-associated proteins.

10. Hydroxylation

    • The addition of hydroxyl groups to specific amino acids, such as proline and lysine.
    • Plays a critical role in collagen stability and function, impacting connective tissue integrity.
    • Involved in the regulation of hypoxia-inducible factors, influencing cellular responses to oxygen levels.