enzyme linked receptor
Summary
An enzyme-linked receptor is a membrane receptor whose intracellular domain is an enzyme or is bound to one. The classic example is the receptor tyrosine kinase, which autophosphorylates tyrosines after ligand binding and starts cascades such as Ras–MAP kinase. Unlike a GPCR, it needs no G protein.
Detail
Meaning: An enzyme-linked receptor is a transmembrane protein whose intracellular domain either is an enzyme or is tightly associated with one. The best-known type is the receptor tyrosine kinase (RTK), used by insulin and many growth factors. Ligand binding brings two receptor subunits together, or shifts a preformed dimer as in the insulin receptor, and the kinase domains phosphorylate tyrosines on each other (autophosphorylation). The phosphotyrosines become docking sites for adaptor proteins, which often activate Ras and the MAP kinase cascade, ending in changes in gene expression and cell division. Other types include receptor guanylyl cyclases and cytokine receptors bound to JAK kinases.
On the MCAT: A passage describes a growth factor and a mutant receptor or mutant Ras. Predict the result: a constitutively active receptor or Ras promotes uncontrolled proliferation, while a kinase-dead receptor blocks the signal. You may also be asked to compare it with GPCRs and ligand-gated ion channels.
Common confusion: Students mix up RTKs and GPCRs. A GPCR has seven transmembrane helices and signals through a G protein and second messengers. A typical RTK has a single transmembrane helix, carries its own kinase activity, and uses no G protein. Its kinase phosphorylates tyrosine, not serine or threonine.
Sources
- Lehninger Principles of Biochemistry
- Molecular Biology of the Cell
- Biochemistry (Berg, Tymoczko, Gatto, Stryer)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.