An Allosteric Mechanism for Activation of the Kinase Domain of Epidermal Growth Factor Receptor
Summary: The mechanism by which the epidermal growth factor receptor (EGFR) is activated upon dimerization has eluded definition. We find that the EGFR kinase domain can be activated by increasing its local concentration or by mutating a leucine (L834R) in the activation loop, the phosphorylation of which is not required for activation. This suggests that the kinase domain is intrinsically autoinhibited, and an intermolecular interaction promotes its activation. Using further mutational analysis and crystallography we demonstrate that the autoinhibited conformation of the EGFR kinase domain resembles that of Src and cyclin-dependent kinases (CDKs). EGFR activation results from the formation of an asymmetric dimer in which the C-terminal lobe of one kinase domain plays a role analogous to that of cyclin in activated CDK/cyclin complexes. The CDK/cyclin-like complex formed by two kinase domains thus explains the activation of EGFR-family receptors by homo- or heterodimerization.
Figures (Click on the small image to view the bigger one):
Figure 1. Ligand-Induced Dimerization of EGFR and Active and Inactive States of Its Kinase Domain
- General view of the ligand-induced dimerization and activation process of EGFR. The kinase domain
is activated through a previously unknown mechanism.
- Detailed view of the catalytic site of the EGFR kinase domain in the active conformation. Leu834 and
L837 are surface exposed and the Lys721/Glu738 ion pair is intact in this conformation.
- Detailed view of the catalytic site in the inactive conformation. Leu834 and L837 pack against
helix αC, preventing the formation of the Lys721/Glu738 ion pair. The right panel shows the
electron density around residues 834–838 for the V924R kinase domain mutant, at 3σ from
a simulated annealing omit map with coefficients (|Fo|
iαc, where the calculated structure factors are generated from a model that does not
contain these residues. The structures shown in (B) and (C) were determined in the absence of drug
molecules as part of this work and are similar to structures determined previously in complex with the
drugs Erlotinib and Lapatinib, respectively (Stamos et al., 2002; Wood et al., 2004).
Figure 2. Catalytic Activity of the Wild-Type EGFR Kinase Domain and Various Mutants in Solution and Attached to Lipid Vesicles
- Catalytic efficiency (kcat/KM)
of the wild-type and mutants of the EGFR kinase domain in solution (yellow) and linked to vesicles (blue).
Fold-increase of the catalytic efficiency upon attachment to vesicles for each protein is indicated on top of
the blue bars. WT: wild-type kinase domain (residues 672 to 998). WT_no_His: the wild-type EGFR kinase domain
with the (His)6 tag removed. All other proteins in this graph
have an intact (His)6 tag. DOGS-NTA-Ni content of vesicles is
5 mole percent in these experiments. Error bars represent standard errors of the linear fittings.
- Concentration-dependent activation of the wild-type kinase domain upon attachment to lipid vesicles. The
specific activities of the wild-type EGFR kinase domain in solution and with vesicles containing various
mole percentages of DOGS-NTA-Ni are shown. The overall concentration of the protein and DOGS-NTA-Ni lipids
in the bulk solution are kept fixed at 3.5 μM and 12.5 μM, respectively, for all measurements.
Data shown are the means + range of variation from two independent experiments.
Figure 3. Crystal Structures of the EGFR Kinase Domain in the Active and Inactive Conformations
- Crystal structure of the EGFR kinase domain in complex with the ATP analog substrate peptide conjugate.
The kinase adopts an active conformation. Electron density (calculated in the same way as in Figure 1C)
for the ATP moiety of the ATP analog-peptide conjugate and seven residues in the C-terminal tail segment
is shown in yellow.
- Crystal structure of the V924R mutant of the EGFR kinase domain in complex with AMP-PNP. The kinase adopts
a Src/CDK-like inactive conformation. The approximate location of the V924R mutation is indicated.
- Crystal structure of an inactive Src kinase in complex with AMP-PNP (PDB ID: 2SRC).
Figure 4. The Asymmetric CDK/Cyclin-like Crystallographic Dimer of the EGFR Kinase Domain
- Overview of the asymmetric dimer, and comparison with the structure of the CDK2/cyclinA complex (PDB ID: 1HCL).
- Detailed view of the asymmetric dimer interface. Monomer A (the activated kinase) is shown in
surface representation in the first exploded view. Hydrophobic interfacial residues from monomer B
are highlighted. In the second exploded view monomer B (the cyclin-like kinase) is shown in surface
representation, and hydrophobic interfacial residues from monomer A are highlighted.
Figure 5. The Symmetric Electrostatic Dimer Is Not Important for EGFR Activation
- Residues involved in the symmetric dimer interface. The two monomers are moved away and rotated
relative to each other as indicated to provide a clearer view of residues involved in the dimer
interface. Blue: residues in the C-terminal tail segment (Glu991 and Tyr992); Cyan: residue in
the N-lobe of the kinase (Lys828); Red: residues in the C-lobe of the kinase (Lys799, Arg938,
Ile942, and Lys946).
- Mutations of interfacial residues in the C-lobe of the kinases, except K799E, do not affect receptor
phosphorylation. The anomalous behavior of K799E is not understood (see Supplemental Data).
Figure 6. The Asymmetric Dimer Interface Is Important for EGFR Activation
- Single mutations at the asymmetric dimer interface abolish EGFR phosphorylation. Stars and circles
denote mutations in the N-lobe and C-lobe face of the dimer interface, respectively.
- Predicted outcomes of a variety of transfection/cotransfection experiments based on the model. Red,
orange, and yellow stars denote mutations in the catalytic site, N-lobe face, and C-lobe face of
the dimer interface, respectively. Different combinations are numbered 1 through 10.
- Results of the transfection/cotransfection experiments. Combination numbers under the transfection
experiments correspond to those in (B).
- Effect of mutations in the asymmetric dimer interface on the catalytic activity of the kinase domain
in solution and attached to lipid vesicles. DOGS-NTA-Ni content of vesicles is 5 mole percent. Fold-increase
of the catalytic activity upon attachment to vesicles for each protein is indicated on top of the blue bars.
Error bars represent standard error of the linear fitting.
Figure 7. A General Model for the Activation of Members of the EGFR Family
- Sequence alignment of the EGFR family members from human and mouse. Two regions containing residues
involved in the N- and C-lobe faces of the dimer interface are shown in the upper and lower panels,
respectively. Identical residues are colored in red. Residues in the N- and C-lobe faces of the dimer
interface are denoted by ovals and triangles, respectively. Magenta and cyan highlight residues in the
dimer interface that are conserved among EGFR, ErbB2, and ErbB4 but not in ErbB3.
- A general model of the activation mechanism for the EGFR family receptor tyrosine kinases. All the
members in the family can act as the cyclin-like activator for the kinase-active members (EGFR, ErbB2,
and ErbB4) after ligand-induced homo- or heterodimerization.
Tables and figures
Coordinates in the Protein Data Bank:
: (Click links to view the full movies)