Polymorphism of the Epidermal Growth Factor Receptor Extracellular Ligand Binding Domain: The Dimer Interface Depends on Domain Stabilization

Epidermal growth factor receptors (EGFRs) and their cytoplasmic tyrosine kinases play important roles in cell proliferation and signaling. The EGFR extracellular domain (sEGFR) forms a dimer upon the binding of ligands, such as epidermal growth factor (EGF) and transforming growth factor a (TGF alpha). In this study, multiple molecular dynamics (MD) simulations of the 2:2 EGF.sEGFR3-512 dimer and the 2:2 TGF alpha.sEGFR3-512 dimer were performed in solvent and crystal environments. The simulations of systems comprising up to half a million atoms reveal part of the structural dynamics of which sEGFR dimers are capable. The solvent simulations consistently exhibited a prominent conformational relaxation from the initial crystal structures on the nanosecond time scale, leading to symmetry breaking and more extensive contacts between the two sEGFR monomers. In the crystal control simulation, this symmetry breaking and compaction was largely suppressed by crystal packing contacts. The simulations also provided evidence that the disordered domain IV of sEGFR may act as a stabilizing spacer in the dimer. Thus, the simulations suggest that the sEGFR dimer can take diverse configurations in solvent environments. These biologically relevant conformations of the EGFR signal transduction network can be controlled by contacts among the structural domains of sEGFR and its ligands.