EGFR Undergoes Ligand-Induced Conformational Changes during Activation

Ligand binding causes EGFR to switch from a closed, inactive state to an open state that exposes a dimerization site to promote EGFR dimerization and signaling. In order to gain insight into the structural dynamics of ligand-mediated EGFR activation and dimerization, crystal structure analysis of different EGFR segments, such as the ligand-binding extracellular domain (ECD) and the intracellular kinase domain (KD), has been the main approach to deduce the different conformations of free and ligand-bound EGFR. Other approaches, such as fluorescence resonance energy transfer and molecular dynamics, have been employed to ascertain the conformational dynamics of EGFR activation in synthetic lipid bilayers, but the dynamics of full-length EGFR activation in their native milieu remain unclear. To ascertain the dynamics of native membrane–bound full-length EGFR before and after ligand activation, Kaplan and colleagues developed a solid-state nuclear magnetic resonance (ssNMR) spectroscopy approach to elucidate the conformational states of EGFR during EGFR activation. Membrane vesicles isolated from a human epidermoid carcinoma cell line which overexpresses EGFR were shown to exhibit high levels of functional EGFR, and ssNMR spectra of [¹³C, ¹⁵N]-labeled membrane vesicles revealed that the addition of EGF induced conformational changes in the EGFR ECD but not the EGFR KD, suggesting that the KD is rigid, whereas the ECD is dynamic. Further, although the ECD of ligand-free EGFR existed in a dynamic structure as an ensemble of different conformers, the ECD of ligand-bound EGFR existed in a rigid open conformation to promote EGFR dimerization. Consistent with these findings, ssNMR supported by dynamic nuclear polarization, which enhances signal intensities in NMR experiments, showed that ligand binding induced the stabilization of EGFR in an open active state. Taken together, these results identify EGFR dynamics within the ECD and provide insight into the ligand-independent activation of EGFR in cancer cells.

Kaplan M, Narasimhan S, de Heus C, Mance D, van Doorn S, Houben K, et al. EGFR dynamics change during activation in native membranes as revealed by NMR. Cell 2016;167:1241–51.e11.

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