Ligand binding induces a conformational change in epidermal growth factor receptor dimers

Abstract

The activation of the epidermal growth factor receptor (EGFR) kinase requires ligand binding to the extracellular domain (ECD). Previous reports demonstrate that the EGFR-ECD can be crystallized in two conformations – a tethered monomer or, in the presence of ligand, an untethered back-to-back dimer. We use Biosensor analysis to demonstrate that even in the monomeric state different C-terminal extensions of both truncated (EGFR_1–501)-ECD and full-length EGFR_1–621-ECD can change the conformation of the ligand-binding site. The binding of a monoclonal antibody mAb806, which recognizes the dimer interface, to the truncated EGFR_1–501-Fc fusion protein is reduced in the presence of ligand, consistent with a change in conformation. On the cell surface, the presence of erythroblastosis B2 (erbB2) increases the binding of mAb806 to the EGFR. The conformation of the erbB2: EGFR heterodimer interface changes when the cells are treated with epidermal growth factor (EGF). We propose that ligand induces kinase-inactive, pre-formed EGFR dimers and heterodimers to change conformation leading to kinase-active tetramers, where kinase activation occurs via an asymmetric interaction between EGFR dimers.

Keywords::

• asymmetric tetramer
• aggregation
• kinase activation
• structural models

Declaration of interest This project was partially funded by NHMRC Program Grant 487922 ‘Colorectal cancer – molecular basis to targeted therapeutics’ and by funds from the Operational Infrastructure Support Program provided by the Victorian Government, Australia. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript. In addition, the manuscript is solely the responsibility of the institutions and individual authors and does not reflect the views of NHMRC. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.