A heterodimer is a protein complex made up of two different subunits, or protein chains, that come together to form a functional unit. These two subunits are not identical, but they work cooperatively to carry out a biological function — often in gene regulation, cell signaling, or enzyme activity.
🔑 Definition:
A heterodimer is a molecular complex consisting of two different polypeptide chains (subunits) that are non-covalently bound and function together as a single biological unit.
🔁 Contrast With:
- Homodimer – a complex of two identical subunits
- Multimer – a complex with more than two subunits (can be same or different)
🧪 Examples in Biology:
✅ NF-κB (p65/p50) Heterodimer
- p65 has a transactivation domain (activates genes)
- p50 binds DNA but lacks a transactivation domain
- Together, they form the classic NF-κB complex that enters the nucleus to regulate genes involved in inflammation and immunity
✅ Receptors (e.g., T-cell receptor, integrins)
- Often composed of two different chains (e.g., α and β subunits)
- Heterodimer structure enables greater diversity and specificity
✅ Transcription Factors
- Many transcription factors (like AP-1) work as heterodimers to expand the range of DNA sequences they can recognize and regulate.
🧠 Why Heterodimers Matter:
| Role | Benefit |
|---|---|
| Functional diversity | Combining two different subunits allows for more flexible functions |
| Regulation | Subunit composition can change in response to signals |
| Stability and specificity | Heterodimer formation can enhance binding or activity |
| Therapeutic targeting | Abnormal heterodimer formation is linked to cancer, inflammation, autoimmune diseases |
🧬 Summary:
A heterodimer is a functional protein pair made of two different subunits. It’s like two unique puzzle pieces coming together to do a job that neither could do alone — particularly in cell communication, gene expression, and immune function.