Domain
Definition and meaning of Domain in chemistry.
Domain, in biochemistry, is a compact, independently folding structural and functional region within a protein's polypeptide chain, typically composed of 50 to 350 amino acids that pack into a stable three-dimensional shape.
In more detail
Domains fold and often function somewhat independently of the rest of the protein, and each usually carries out a specific job, such as binding a ligand, catalyzing a reaction, or mediating protein-protein interactions. Many proteins are built from several domains connected by flexible linkers, allowing modular combinations of functions within one polypeptide. Because domains are evolutionarily mobile units, the same domain type (e.g., a zinc finger or an SH2 domain) recurs across many unrelated proteins, having been reshuffled through gene duplication, fusion, and exon shuffling over evolutionary time.
Key facts
| Field | Biochemistry |
|---|---|
| Typical size | ~50-350 amino acids |
| Folding | Independently stable 3D structure |
| Common examples | SH2, SH3, zinc finger, kinase domains |
Src family tyrosine kinases contain three domains on one chain: an SH3 domain that binds proline-rich sequences, an SH2 domain that binds phosphotyrosine residues, and a catalytic kinase domain that transfers phosphate groups to substrate proteins.
Frequently asked questions
How is a protein domain different from a subunit?
A domain is a folded region within a single polypeptide chain, while a subunit is an entirely separate polypeptide chain that associates with others to form a multi-subunit protein complex.
Can a domain work if separated from the rest of the protein?
Often yes; many domains retain their native fold and function when expressed on their own, which is why they can be shuffled between proteins naturally and used as modular building blocks in protein engineering.