Ubiquitin is a small regulatory protein found in all eukaryotic cells, best known for its role in marking other proteins for destruction. It acts like a molecular tag that labels proteins for various cellular fates — most famously, for degradation by the proteasome.
🔑 Definition:
Ubiquitin is a highly conserved 76–amino acid protein that attaches to other proteins to regulate their stability, location, activity, or interaction with other proteins.
⚙️ What Does Ubiquitin Do?
The process of adding ubiquitin to a protein is called ubiquitination (or ubiquitylation). This happens in a stepwise enzymatic reaction involving:
- E1 – Ubiquitin-activating enzyme
- E2 – Ubiquitin-conjugating enzyme
- E3 – Ubiquitin ligase (gives specificity: it chooses the target protein)
🗑️ Most Well-Known Function:
“Tag and destroy”
When a protein is tagged with a chain of ubiquitins, it signals that the protein should be degraded by the proteasome — the cell’s recycling center.
🔁 Other Functions of Ubiquitin:
Depending on how and where it’s attached, ubiquitin can also:
- Regulate protein activity
- Change protein location (e.g., send it to the nucleus or membrane)
- Signal for DNA repair
- Help control the cell cycle
- Influence immune and inflammatory responses
🧠 Why It Matters:
- Protein quality control: Removes misfolded or damaged proteins
- Prevents disease: Disruption in ubiquitination is linked to:
- Cancer (tumor suppressor proteins not degraded properly)
- Neurodegenerative diseases (like Parkinson’s and Alzheimer’s)
- Autoimmune diseases
- Drug target: Some cancer drugs (e.g., proteasome inhibitors like bortezomib) work by interfering with ubiquitin-regulated protein degradation
📌 Summary:
Ubiquitin is the cell’s molecular “post-it note” — used to tag proteins for destruction or reprogramming. It’s essential for keeping cells healthy by regulating what proteins stay, what goes, and what gets repaired.