In this reaction, FGF receptor in the plasma membrane binds an associating extracellular ligand, a requisite step for subsequent activation. The resulting complex consists of dimerized receptor, two ligand molecules, and heparan sulfate. NCAM and other members of the CAM protein family directly or indirectly modulate this interaction in a variety of neural tissues. The details of this interaction in vivo have not been definitively established at the molecular level, but are thought to play a central role in the regulation of the development of these tissues. Also, TGFBR3 (beta-glycan) facilitates the binding of FGF2 with its receptor FGFR1 by binding with FGF2 itself and bringing more ligands into receptor proximity (Andres et al. 1992, Knelson et al. 2013).