The fibroblast growth factor receptors (FGFR) are, as their name implies, receptors that bind to members of the fibroblast growth factor (FGF) family of proteins.
[3] These isoforms vary in their ligand-binding properties and kinase domains, however all share the common extracellular region composed of three immunoglobulin(Ig)-like domains (D1-D3), and thus belong to the immunoglobulin superfamily.
[5] This "acid box" can participate in the regulation of FGF binding to the FGFR.
In many cases, the FGFs themselves can also activate more than one receptor (i.e., FGF1, which binds all seven principal FGFRs[6]).
So far, five distinct membrane FGFR have been identified in vertebrates and all of them belong to the tyrosine kinase superfamily (FGFR1 to FGFR4).