Ligand-binding enhances the affinity of dimerization of the extracellular domain of the epidermal growth factor receptor.

We studied the dimerization of the recombinant soluble extracellular domain of the epidermal growth factor receptor (sEGFR) in response to EGF-binding using multi-angle laser light scattering with size exclusion chromatography (SEC-MALLS). In the absence of EGF, sEGFR behaved as a monomer. However, upon EGF-binding, sEGFR formed a dimer with the stoichiometry of two EGF molecules bound to two sEGFR molecules [(EGF)2-(sEGFR)2]. We analyzed the chemical equilibrium of the dimer formation by SEC-MALLS using a dissociation constant of 0.25 microM for the binding of EGF to sEGFR. The calculated dissociation constant for EGF-induced sEGFR dimerization was found to be 2.4 +/- 0.9 microM. These experiments demonstrated that EGF induces receptor dimerization and that two EGF molecules are bound to an EGF-receptor dimer.