Structural Analysis of the Mechanism of Inhibition and Allosteric Activation of the Kinase Domain of HER2 Protein

Abstract

Aberrant signaling of ErbB family members human epidermal growth factor 2 (HER2) and epidermal growth factor receptor (EGFR) is implicated in many human cancers, and HER2 expression is predictive of human disease recurrence and prognosis. Small molecule kinase inhibitors of EGFR and of both HER2 and EGFR have received approval for the treatment of cancer. We present the first high resolution crystal structure of the kinase domain of HER2 in complex with a selective inhibitor to understand protein activation, inhibition, and function at the molecular level. HER2 kinase domain crystallizes as a dimer and suggests evidence for an allosteric mechanism of activation comparable with previously reported activation mechanisms for EGFR and HER4. A unique Gly-rich region in HER2 following the ␣-helix C is responsible for increased conformational flexibility within the active site and could explain the low intrinsic catalytic activity previously reported for HER2. In addition, we solved the crystal structure of the kinase domain of EGFR in complex with a HER2/EGFR dual inhibitor (TAK-285). Comparison with previously reported inactive and active EGFR kinase domain structures gave insight into the mechanism of HER2 and EGFR inhibition and may help guide the design and development of new cancer drugs with improved potency and selectivity.

A single ligand is sufficient to activate EGFR dimers

“…Unlike Drosophila EGFR, ligand binding is not required for ErbB2 to participate in active signaling complexes owing to the presence of ligand-binding homologs, which allowed ErbB2 to evolve a fixed straight domain II conformation and specialize as a heterodimerization partner. ErbB2 activation in cases of pathological overexpression thus seems likely to be mediated by intracellular regions (25,26). Curiously, a weak dimer of unliganded dmEGFR that looks similar to the leftmost dimer in Fig.…”

Acquired Substrate Preference for GAB1 Protein Bestows Transforming Activity to ERBB2 Kinase Lung Cancer Mutants

“…ERBB2 kinase mutations in the ␣C-␤4 region have been identified in non-small cell lung cancers (7,8). Our previous work has demonstrated that the unique glycine-rich ␣C-␤4 loop plays a critical autoinhibitory role in control of the ERBB2 kinase activity (9), and this observation has been verified by a recent crystallographic structure (10). An earlier work revealed that the most common oncogenic ERBB2 mutation with an in-frame duplication of four residues YVMA before Gly-776 (ERBB2 YVMA ) has increased autokinase activity and is more potent than wild type (WT) kinase in cell signaling and tumorigenicity (11).…”

“…Upon dimer formation, the helix ␣C of one kinase domain is restrained to the catalytically competent conformation by the C-lobe of the other. The proper orientation of ␣C helix for kinase activation in EGFR and ERBB4 is highly controlled through hydrogen bonds and hydrophobic interactions of residues in the ␣C-␤4 loop with residues in the activation loop and the C-lobe (10). Conversely, the unique Gly-rich ␣C-␤4 region in ERBB2 fails to form these interactions and imparts greater flexibility to the enzyme active site.…”

Destabilization of the Epidermal Growth Factor Receptor (EGFR) by a Peptide That Inhibits EGFR Binding to Heat Shock Protein 90 and Receptor Dimerization

“…In a recent crystallographic study of the kinase domain of EGFR in complex with a dual EGFR/HER2 inhibitor, TAK-285, the eight-amino acid segment, was shown to be located on the surface of EGFR at the heterodimerization interface (23). The initial SVDN in the eight-amino acid segment is thought to play a critical role in kinase activation (24).…”