Direct Measurements of Differential FGF Binding to Full-Length FGFRs in Plasma Membrane Derived Vesicles

The strength of ligand binding to membrane receptors has long been recognized as a critical factor in signal transduction. However, measurements of receptor tyrosine kinase binding are predominantly conducted using isolated extracellular domains rather than full-length receptors. Here, we explore the utility of a methodology that allows the quantification of both receptor concentration and bound ligand concentration in the membrane of cell-derived vesicles. Measurements for the ligands FGF1 and FGF2, binding to the receptors FGFR1 and FGFR2, reveal striking unexpected differences in the stoichiometry and the apparent cooperativity of the binding reactions. These novel insights underscore the significance of maintaining native geometries and functionalities in ligand binding assays.