A multimer is a complex of multiple subunits (proteins or molecules) that are non-covalently or covalently bound together to function as a single biological unit. These subunits can be identical or different, and the entire structure plays roles in structural support, signaling, enzymatic activity, and more.
🔑 Definition:
A multimer is an assembly of more than two monomer units (individual molecules or proteins) that come together to form a larger, functional complex.
🧩 Types of Multimers:
| Type | Composition | Example |
|---|---|---|
| Homomultimer | Made of identical subunits | Hemoglobin α2β2 (each chain type is duplicated) |
| Heteromultimer | Made of different subunits | Antibodies (2 heavy + 2 light chains) |
| Dimer | 2 subunits (can be homo- or hetero-) | Transcription factor dimers (e.g., p65/p50) |
| Trimer, Tetramer, Pentamer… | 3, 4, 5… subunits | G-protein (trimer), IgM (pentamer) |
🧪 Biological Examples of Multimers:
- Hemoglobin
- A tetramer of two α and two β globin subunits
- Carries oxygen in the blood
- Antibodies (Immunoglobulins)
- Typically tetramers (2 heavy and 2 light chains)
- Can form pentamers (IgM) or dimers (IgA)
- Ion Channels
- Often made of 4 or more subunits that form a pore through the cell membrane
- Viral Capsids
- Multimers of protein units form a protective shell around viral RNA/DNA
🧠 Why Multimers Matter:
| Function | Importance |
|---|---|
| Structural stability | Multimeric complexes are often more stable than monomers |
| Functional specialization | Different subunits can play unique roles (e.g., catalysis, regulation) |
| Cooperative behavior | Subunits can work together for enhanced or regulated activity |
| Signal integration | In cell receptors, multimers can detect and transmit signals |
📌 Summary:
A multimer is a complex made of multiple individual subunits, working together to carry out a biological function. Whether identical or mixed, these assemblies are essential in proteins, receptors, antibodies, enzymes, and structural elements across all living systems.