File:FGFR receptor subtype.jpeg

FGFRs are comprised of 3 immunoglobulin domains (IgI-III), with IgIII being the closest to the transmembrane, and IgI being the furthest away. Some features of this receptor include an acidic box (AD) located in-between IgI and IgII, a heparin-binding domain (HBD) within IgII which is important in signal transduction, and that IgIII is a transmembrane (TM) structure with kinase and interkinase domains (KD and IKD) within the intracellular space. FGF ligands linked to heparin sulfate proteoglycan (HSPG) bind to both the IgII and IgIII domain of the receptor (with the heparin component specificially binding to IgII) resulting in dimerisation of the receptors and activation of signal transduction pathways through the phosphorylation of tyrosine residues, as discussed in more detail under the subheading signal transduction.