IDENTIFICATION OF THE EXTRACELLULAR DOMAINS OF FLT-1 THAT MEDIATE LIGAND INTERACTIONS

Vascular Endothelial Growth Factor (VEGF) mediates its actions through the Flt-1 and KDR(Flk-1) receptor tyrosine kinases, To localize the e xtracellular region of Flt-1 that is involved in ligand interactions, we prepared secreted fusion proteins between various combinations of i ts seven extracellular IgG-Like folds, Ligand binding studies show tha t in combination, domains one and two (amino acids 1-234) are sufficie nt to achieve VEGF(165) interactions, Either domain alone is insuffici ent to achieve this effect, However, Scatchard analysis reveals that d espite the binding capabilities of this construct, the Kd is five fold lower than ligand binding to the full extracellular domain. We find t hat addition of domain. three to this minimal site restores high affin ity receptor binding, Further, we show that domains one and two are su fficient to achieve interactions of Flt-1 with Placental Growth Factor (PIGF-1). (C) 1997 Academic Press.