Structural analyses of the extracellular region of stem cell factor (SCF)
receptor (also designated KIT) in complex with SCF revealed a sequence motif in
a loop in the fourth Ig-like domain (D4) that is responsible for forming
homotypic receptor contacts and for ligand-induced KIT activation and cell
signaling. An identical motif was identified in the most membrane-proximal
seventh Ig-like domain (D7) of vascular endothelial growth factor receptor 1
(VEGFR1), VEGFR2, and VEGFR3. In this report we demonstrate that ligand-induced
tyrosine autophosphorylation and cell signaling via VEGFR1 or VEGFR2 harboring
mutations in critical residues (Arg726 or Asp731) in D7 are strongly impaired.
We also describe the crystal structure of D7 of VEGFR2 to a resolution of 2.7 A.
The structure shows that homotypic D7 contacts are mediated by salt bridges and
van der Waals contacts formed between Arg726 of one protomer and Asp731 of the
other protomer. The structure of D7 dimer is very similar to the structure of D4
dimers seen in the crystal structure of KIT extracellular region in complex with
SCF. The high similarity between VEGFR D7 and KIT D4 in both structure and
function provides further evidence for common ancestral origins of type III and
type V RTKs. It also reveals a conserved mechanism for RTK activation and a
novel target for pharmacological intervention of pathologically activated RTKs.
Figure 3.
Structure of VEGFR2 D7 homodimer. (A) A ribbon diagram and a
transparent molecular surface of D7 homodimer structure (side
view). Asp731 and Arg726 are shown as a stick model. (B) A close
view of the homotypic D7 interface of the two neighboring
molecules (pink and green). Salt bridges formed between Asp731
and Arg726 are shown as dashed lines. (C) Charge distribution of
D7 homodimer (side view) is shown as a surface potential model
(Left). View of D7 surface that mediates homotypic contacts
(Right). (D) 2F[o]-F[c] electron density map contoured at 1.1σ
level showing a view of the D7–D7 interface. The backbones of
VEGFR D7 protomers are represented as pink and yellow tubes,
respectively.
Figure 4.
Superposition of the structure of D7 of VEGFR2 with the
structure of D4 of dimeric KIT-SCF complex. Overlay of VEGFR D7
structure (PDB ID code: 3KVQ) and the structure of KIT dimer in
complex with SCF (PDB ID code: 2E9W) (Left). A closer view of
superimposed D7 and D4 regions reveals high similarity in domain
arrangement and homotypic contacts (Right). VEGFR2 D7 is
illustrated in green and the EF loop is in yellow. D4 of KIT is
illustrated in gray and its EF loop is in orange.
