Role of glycosylation in EGFR ectodomain interactions : a molecular dynamics study
Azimzadeh Irani, Maryam
Date of Issue2017-05-23
School of Biological Sciences
The Epidermal Growth Factor Receptor (EGFR) is a tyrosine kinase protein, overexpressed in several cancers. The extracellular domain of EGFR is heavily glycosylated with sugar moieties of varying compositions. Growth factor (mostly Epidermal Growth Factor or EGF) binding activates EGFR. This occurs by inducing the transition from the autoinhibited tethered conformation to an extended conformation of the monomeric form of EGFR and by stabilizing the flexible pre-formed dimer. Several antibodies inhibit EGFR by targeting the growth factor binding site or the dimeric interfaces. Activated EGFR adopts a back-to-back dimeric conformation after binding of another homologous receptor to its extracellular domain as the dimeric partner. Atomistic MD simulations show that glycosylation of the EGFR extracellular domain play critical roles in the binding of growth factors, monoclonal antibodies and the dimeric partners to the monomeric EGFR extracellular domain. N-glycosylation favors growth factor binding to EGFR by a combinatorial mechanism of hydrogen bonding, non-bonded interactions and several intramolecular contacts. Glycosylation also plays distinct roles in binding of antibodies to spatially separated epitopes of the EGFR extracellular domain and assist in maintaining the dimeric interfaces. In the activation process of EGFR, N-glycosylation reduces the flexibility of the tethered and extended monomeric forms of EGFR extracellular domain. By supporting the glycosylated form of the extended state and weakening the tethering interactions in the tethered state, glycosylation supports the extended conformation and facilitates the tethered-extended transition. Dimerization of the EGFR extracellular domain is regulated by attached N-glycans which decrease the flexibility of the dimeric conformation. The decrease in flexibility results in increases in intramonomeric turn motions and intradimeric twist motions which likely induces the asymmetric arrangements of the transmembrane and subsequently the intracellular kinase domains which triggers the signaling cascade in the cystosol.