Biological activity and phosphorylation sites of the bacterially expressed cytosolic domain of the KDR VEGF-receptor.

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor which binds to two structurally similar receptor tyrosine kinases, KDR and FLT1. Towards the goal of clarifying the signal transduction pathways by which VEGF activates endothelial cells, we expressed in bacteria an enzymatically active form of the cytosolic domain of the KDR receptor. The expressed protein undergoes autophosphorylation in both bacterial cells and in its purified form. Using peptide mapping and sequencing of peptides, we identified four tyrosine residues that are phosphorylated corresponding to residues 951, 996, 1054, and 1059 of the KDR protein. The location of the phosphorylated residues in the bacterially expressed protein, and/or the consensus sequences around these sites, suggest they may be identical to the phosphorylated sites of KDR in mammalian cells.