Cysteine 116 participates in intermolecular bonding of the human VEGF121 homodimer

VEGF121, the 121-amino acid form of vascular endothelial growth factor is a homodimer with nine cysteine residues per monomer. While three intramolecular and two intermolecular disulfide bonds have been mapped, the state of the ninth cysteine, Cys116, is not known. In this study, we determined that human VEGF121 contains a third interchain disulfide bond between Cys116 of each monomer. We also isolated a VEGF121 variant with two extra cysteines bound to each Cys116. No evidence was found for the exsistence of Cys116 in the reduced state. In fact, selective reduction of the Cys116 interchain disulfide bond yielded an unstable VEGF121 molecule, which reoxidized quickly. Biological activities of VEGF121 Cys116 variants were assessed. The oxidative state of Cys116 has no effect on binding or proliferation activities but may be important for overall stability of the molecule.