Table 1.
Classification and characteristics of the human RTKs.
| Class | Family name | Members | Molecular characteristics of the extracellular domains |
|---|---|---|---|
| I | EGFR | EGFR, ERBB2, ERBB3, ERBB4 | 2 cysteine-rich domains |
| II | Insulin R | INSR IGFR | 2 chains α and β, with one cysteine-rich and 2 FNIII domains |
| III | PDGFR | PDGFRα, PDGFRβ, M-CSFR, KIT, FLT3L | 5 Ig-like domains |
| IV | VEGFR | VEGFR1, VEGFR2, VEGFR3 | 7 Ig-like domains |
| V | FGFR | FGFR1, FGFR2, FGFR3, FGFR4 | 3 Ig-like domains, 1 acidic box |
| VI | CCK | CCK4 | 7 Ig-like domains |
| VII | NGFR | TRKA, TRKB, TRKC | 2 Ig-like domains, rich leucin domains |
| VIII | HGFR | MET, RON | 1 transmenbrane α chain linked with one extracellular β chain |
| IX | EPHR | EPHA1 to 6, EPHB1 to 6 | 1 Ig-like, 1 cysteine-rich and 2 FNIII-like domains |
| X | AXL | AXL, MER, TYRO3 | 2 Ig-line, 2 FNIII-like domains |
| XI | TIE | TIE, TEK | 2 Ig-like, 1 EGF, and 3 FNIII-like domains |
| XII | RYK | RYK | 1 transmenbrane β chain linked with one extracellular α chain |
| XIII | DDR | DDR1, DDR2 | 1 discoidin-like domain |
| XIV | RET | RET | 1 cadherin-like domain |
| XV | ROS | ROS | 6 FNIII-like domains |
| XVI | LTK | LTK, ALK | 1 cysteine-rich domain |
| XVII | ROR | ROR1, ROR2 | 1 Ig-domain, 1 cysteine-rich domain and one kringle-like domains |
| XVIII | MUSK | MUSK | 4 Ig-like and 1 cysteine-rich domains |
| XIX | LMR | AATYK1, AATYK2, AATYK3 | A short extracellular domain |
| XX | Undetermined | RTK106 | A short receptor chain with a short extracellular domain |
EGFR: epidermal growth factor receptor; InsR: insulin receptor; PDGFR: platelet-derived growth factor receptor; VEGFR: vascular endothelial growth factor receptor; FGFR: fibroblast growth factor receptor; CCK: colon carcinoma kinase; NGFR, nerve growth factor receptor; HGFR: hepatocyte growth factor receptor; EphR: ephrin receptor; Axl: from the Greek word anex-elekto, or uncontrolled, a Tyro3 protein tyrosine kinase; TIE: tyrosine kinase receptor in endothelial cells; RYK: receptor related to tyrosine kinases; DDR: discoidin domain receptor; Ret: rearranged during transfection; ROS: RPTK expressed in some epithelial cell types; LTK: leukocyte tyrosine kinase; ROR: receptor orphan; MuSK: muscle-specific kinase; LMR: Lemur; Ig: immunoglobulin; FN: fibronectin. (From Blume-Jensen and Hunter [10]).