Vascular endothelial growth factors (
VEGFs) regulate blood and lymph vessel formation through activation of three
receptor tyrosine kinases,
VEGFR-1, -2, and -3. The extracellular domain of
VEGF receptors consists of seven
immunoglobulin homology domains, which, upon
ligand binding, promote receptor dimerization. Dimerization initiates transmembrane signaling, which activates the intracellular
tyrosine kinase domain of the receptor.
VEGF-C stimulates lymphangiogenesis and contributes to
pathological angiogenesis via
VEGFR-3. However, proteolytically processed
VEGF-C also stimulates
VEGFR-2, the predominant transducer of signals required for physiological and
pathological angiogenesis. Here we present the crystal structure of
VEGF-C bound to the
VEGFR-2 high-affinity-binding site, which consists of
immunoglobulin homology domains D2 and D3. This structure reveals a symmetrical 22 complex, in which left-handed twisted receptor domains wrap around the 2-fold axis of
VEGF-C. In the
VEGFs, receptor specificity is determined by an N-terminal alpha helix and three
peptide loops. Our structure shows that two of these loops in
VEGF-C bind to
VEGFR-2 subdomains D2 and D3, while one interacts primarily with D3. Additionally, the N-terminal helix of
VEGF-C interacts with D2, and the groove separating the two
VEGF-C monomers binds to the D2/D3 linker.
VEGF-C, unlike
VEGF-A, does not bind
VEGFR-1. We therefore created VEGFR-1/VEGFR-2 chimeric
proteins to further study receptor specificity. This biochemical analysis, together with our structural data, defined
VEGFR-2 residues critical for the binding of
VEGF-A and
VEGF-C. Our results provide significant insights into the structural features that determine the high affinity and specificity of
VEGF/VEGFR interactions.