Figure 7.

Effect of gangliosides on the binding of FGF-2 to soluble xcFGFR-1. (A) ¹²⁵I-FGF-2 (0.3 pmol) was incubated for 2 h at 37°C with 3 pmol of recombinant, soluble xcFGFR-1 in the absence (ctrl) or in the presence of 1.5 nmol of the indicated gangliosides. Then, ¹²⁵I-FGF-2–xcFGFR-1 complexes were chemically cross-linked with BSOCOES and analyzed by 10% SDS-PAGE followed by autoradiography of the gel. Arrow points to the cross-linked M_r 69,000 kDa ¹²⁵I-FGF-2–xcFGFR-1 complex (Rusnati et al., 1994), which is abrogated by incubation with a 100-fold excess of unlabeled growth factor (FGF-2). (B) Aliquots (50 μl) containing 1 nmol of BODIPY-12-GM₁ were incubated into plastic dishes coated with 20 μg/ml FGF-2 in the presence of increasing concentrations of xcFGFR-1 (•) or of heparin (○). At the end of incubation, fluorescent GM₁ bound to the immobilized growth factor was extracted, measured with a spectrofluorimeter, and compared with the amount of fluorescent GM₁ bound to immobilized FGF-2 in the absence of the competitor.