The α-helical domain near the amino terminus is essential for dimerization of vascular endothelial growth factor

Vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen and a key mediator of aberrant endothelial cell proliferation and vascular permeability in a variety of human pathological situations such as tumor angiogenesis, diabetic retinopathy, or psoriasis, By amino-terminal deletion analysis and by site-directed mutagenesis we have identified a new domain within the amino-terminal alpha-helix that is essential for dimerization of VEGF. VEGF(121) variants containing amino acids 8 to 121 or 14 to 121, respectively, either expressed in Escherichia coli and refolded in vitro, or expressed in Chinese hamster ovary cells, were in a dimeric conformation and showed full binding activity to VEGF receptors and stimulation of endothelial cell proliferation as compared with wild-type VEGF, In contrast, a VEGF(121) variant covering amino acids 18 to 121, as well as a variant in which the hydrophobic amino acids Val(14), Val(15), Phe(17), and Met(18) within the amphipathic alpha-helix near the amino terminus were replaced by serine, failed to form biological active VEGF dimers, From these data we conclude that a domain between amino acids His(12) and Asp(19) within the aminoterminal alpha-helix is essential for formation of VEGF dimers, and we propose hydrophobic interactions between VEGF monomers to stabilize or favor dimerization.