Themes in Signaling   Molecular surface representation of a top view of a dimeric FGF2-FGFR1 complex. FGF2 is in orange and D2 of the extracellular ligand-binding domain is in green. The side chains of heparin binding reside on FGF2 and D2 are rendered in ball-and-stick. The ordered sulfate ions bound to FGF2 and D2 are also shown. (Same view as in the previous image)