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

Abstract

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 α-helix that is essential for dimerization of VEGF. VEGF121 variants containing amine 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 VEGF121 variant covering amine acids 18 to 121, as well as a variant in which the hydrophobic amine acids Val14, Val15, Phe17, and Met18 within the amphipathic α-helix near the amine terminus were replaced by serine, failed to form biological active VEGF dimers. From these data we conclude that a domain between amine acids His12 and Asp19 within the amino-terminal α-helix is essential for formation of VEGF dimers, and we propose hydrophobic interactions between VEGF monomers to stabilize or favor dimerization.