Catalytically inactive phospholipase A2 homologue binds to vascular endothelial growth factor receptor-2 via C-terminal loop region

Abstract

VEGF (vascular endothelial growth factor) regulates neovascularization through binding to its receptorKDR(kinase insert domaincontaining receptor; VEGF receptor-2). We recently identified a catalytically inactive PLA2 (phospholipase A2) homologue (KDR-bp) in the venom of eastern cottonmouth (Agkistrodon piscivorus piscivorus) as a third KDR-binding protein, in addition to VEGF165 and tissue inhibitor of metalloproteinase-3. KDR-bp binds to the extracellular domain of KDR with a Kd of 10−8 M, resulting in specific blockade of endothelial cell growth induced by VEGF165. Inactive PLA2 homologues are widely distributed in the venoms of Viperidae snakes and are known to act as myotoxins. In the present study, we demonstrated that KDRbinding ability is a common characteristic for inactive PLA2 homologues in snake venom, but not for active PLA2s such as neurotoxic and platelet aggregation-modulating PLA2s. To understand better the KDR and KDR-bp interaction, we resolved the binding region of KDR-bp using eight synthetic peptides designed based on the structure of KDR-bp. A synthetic peptide based on the structure of the C-terminal loop region of KDRbp showed high affinity for KDR, but other peptides did not, suggesting that the C-terminal loop region of KDR-bp is involved in the interaction with KDR. The results of the present study provide insight into the binding of inactive PLA2 homologues to KDR, and may also assist in the design of novel anti-KDR molecules for anti-angiogenic therapy.