= Receptor tyrosine kinase
{wiki}
= RTK
{c}
{synonym}
A <receptor tyrosine kinase> combines extracellular <ligand> recognition with an intracellular <protein kinase> <protein domain>. A membrane-spanning segment connects these parts across the <cell membrane>: the signal changes the intracellular machinery without requiring the <ligand> to enter the <cytosol>. The <protein kinase> transfers a <phosphate> group from <ATP> to selected <tyrosine residues> on <proteins>, including the <receptor> itself.<Molecular Biology of the Cell, 4th edition by Bruce Alberts and others/Signaling through Enzyme-Linked Cell-Surface Receptors>[“Activated Receptor Tyrosine Kinases Phosphorylate Themselves”: extracellular binding, intracellular catalytic domains and ATP-dependent phosphate transfer]{ref}
This architecture makes a reception event useful in two ways: it can change catalytic activity and assemble a local group of signaling <proteins>. <Trans-autophosphorylation> can create <phosphotyrosine residues> recognized by <SH2 domains>. Recruitment positions a downstream <enzyme> or relay <protein> near its partners. Neither every modified site nor every recruited <protein> has the same effect; association is a specific molecular connection, rather than a universal command to activate everything nearby.<Molecular Biology of the Cell, 4th edition by Bruce Alberts and others/Signaling through Enzyme-Linked Cell-Surface Receptors>[“Phosphorylated Tyrosines Serve as Docking Sites For Proteins With SH2 Domains”, Figure 15-53: signaling enzymes, adaptors and negative regulators]{ref}
Compare the <epidermal growth factor receptor> with the <insulin receptor>. Their common topology does not impose one activation geometry or make assembly equivalent to activity. The <receptor phosphorylation assay> consequently needs more than evidence that two <protein> chains associate.
\Image[/receptor-tyrosine-kinase-activation-architectures.png]
{title=<Receptor tyrosine kinase> architecture and distinct activation mechanisms}
{description=Original topology cartoons contrasting <EGFR> with the preassembled <insulin receptor>. Orange dots mark <phosphotyrosine residues>; S–S marks <protein disulfide bonds>. The <EGFR> panel separates asymmetric catalytic contact from partner-tail <phosphorylation>. Shapes, distances and drawn <ligand> counts are explanatory, rather than atomic structures or binding stoichiometry.}
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