domain
Summary
A domain is a compact region of a single polypeptide that folds into a stable unit and often carries a specific function, such as binding a ligand, binding DNA, spanning a membrane or catalysis. Many domains can fold independently, so deleting or mutating one tends to disrupt that function.
Detail
Meaning: A domain is a compact, stably folded region of one polypeptide, typically tens to a few hundred residues, built from α helices and β sheets held together by tertiary interactions: the hydrophobic effect, hydrogen bonds, ionic interactions and disulfide bonds. Many domains can fold on their own and keep their function when separated from the rest of the chain. Multidomain proteins join these units with flexible linkers, for example a ligand-binding domain, a transmembrane domain and a catalytic domain in one receptor. In Biology, domain also means the highest taxonomic rank (Bacteria, Archaea, Eukarya).
On the MCAT: A passage describes a transcription factor, receptor or enzyme with named domains. You predict the effect of a deletion or mutation: removing a DNA-binding domain abolishes DNA binding, while an activation domain may stay intact. Transmembrane domains are rich in nonpolar residues, whereas domains exposed to water are richer in polar and charged ones.
Common confusion: A domain is not a subunit, which is a separate polypeptide chain in quaternary structure, and not a motif, which is a small recurring supersecondary pattern such as a helix-turn-helix. It is also not the same as an active site, which is a few residues that may come from distant parts of the sequence and can sit between domains.
Sources
- Lehninger Principles of Biochemistry
- Biochemistry (Berg, Tymoczko, Gatto, Stryer)
- Biochemistry (Voet and Voet)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.