Dimer interface of transmembrane domains for neu/erbB-2 receptor dimerization and transforming activation: a model revealed by molecular dynamics simulations.

The specific point mutation Val-->Glu664 within the transmembrane domain of the neu/erbB-2 receptor is associated with increased receptor dimerization and increased receptor tyrosine kinase activity resulting in malignant transformation of cells. It is well established that Glu and residues in proximity are necessary for receptor dimerization but many studies suggest that other intramembrane constraints, not yet elucidated, are determinant for transformation. In this work, we investigated dimer models both to understand the structural role of the Glu mutation in the transmembrane domain association and to determine helix-helix contacts required for oncogenic transformation. Different types of helix-helix association based on data resulting from Cys mutational studies of the full wild receptor and spectroscopic data of transmembrane neu peptides have been explored by molecular dynamics simulations. The study leads to propose a model for the dimeric association of the transmembrane domains of the oncogenic neu receptor showing left-handed interactions of the two helices stabilized by symmetrical hydrogen bonding interactions involving the Glu side chain on one helix and the facing carbonyl of Ala661 on the second helix. Contacting residues observed in the symmetric interface explain the transforming activity or the non transforming activity of many neu mutants. Moreover the left-handed coiled coil structure is fully consistent with recent results proving the role of rotational linkage of the transmembrane domain with the kinase domain. Comparison between the predicted dimer model and those presumed from experiments strongly suggests helix flexibility in the extracellular juxtamembrane region.