Receptor (biochemistry) - Structure

Structure

The structures of receptors are very diverse and can broadly be classified into the following categories:

• peripheral membrane proteins
• transmembrane proteins
  • G protein-coupled receptors – Composed of seven transmembrane alpha helices. The loops connecting the alpha helices form extracellular and intracellular domains. The binding site for larger peptidic ligands is usually located in the extracellular domain whereas the binding site for smaller non-peptidic ligands is often located between the seven alpha helices and one extracellular loop.
  • ligand-gated ion channels – Have a heteropentameric structure. Each subunit of consist of the extracellular ligand-binding domain and a transmembrane domain where the transmembrane domain in turn includes four transmembrane alpha helixes. The ligand binding cavities are located at the interface between the subunits.
  • receptor tyrosine kinase – Functional receptors are homodimers. Each monomer possesses a single transmembrane alpha helix and an extracellular domain containing the ligand binding cavity and an intracellular domain with catalytic activity.
• soluble globular proteins
  • nuclear receptors – Composed of a C-terminal DNA-binding domain (DBD) and a N-terminal ligand-binding domain (LDB). The LBD is composed of twelve alpha helices and an antiparallel beta sheet. The ligand binding cavity is buried within the interior of the LBD.

Membrane receptors may be isolated from cell membranes by complex extraction procedures using solvents, detergents, and/or affinity purification.

The structures and actions of receptors may be studied by using biophysical methods such as X-ray crystallography, NMR, circular dichroism, and dual polarisation interferometry. Computer simulations of the dynamic behavior of receptors have been used to gain understanding of their mechanism of action.