Trans-Membrane Linked Receptors
An enzyme linked-receptor, also known as catalytic receptor, is a transmembrane receptor, where the binding of an extracellular ligand causes enzymatic activity on the intracellular side. Hence, a catalytic receptor is an integral membrane protein possessing both enzymatic catalytic and receptor functions. They have two important domains: an extracellular-ligand binding domain and an intracellular domain, which has a catalytic function, and a transmembrane helix. The signalling molecule binds to the receptor on outside of the cell and causes a conformational change on the catalytic function located on the receptor inside the cell.
Some examples of the enzyme-linked receptor are as follows:
• Receptor tyrosine kinase, as in fibroblast growth factor receptor. Most enzymelinked receptors are of this type.
• Serine/threonine-specific protein kinase, as in bone morphogenic protein
• Guanylate cyclise, as in atrial natriuretic factor receptor
Following major families of catalytic receptors are known:
• Erb (Epidermal growth factor receptor)
• GDNF (glial cell-derived) neurotrophic factor
• NPR (natriuretic peptide receptor)
• trk neurotrophin receptor
• Toll-like receptor (TLR)
Out of these five types, only in case of NPR, catalytic activity is involved with the enzyme gaunylyl cyclase (EC 4.6.1.2). In all other types, the enzyme involved is tyrosine kinase (EC 2.7.10.1). For every type of receptor, there are different members, genes and ligands.
