The gamma-carboxyglutamic acid domain of human factor VIIa is essential for its interaction with cell surface tissue factor.

Abstract

Previous studies indicated that both plasma-derived and recombinant human factor VIIa specifically interacted with tissue factor on the surface of a human bladder carcinoma cell line (J82). In the presence of calcium ions, factor VIIa interacted with approximately 300,000 binding sites/cell with a dissociation constant (Kd) of 3.25 nM (Sakai, T., Lund-Hansen, T., Paborsky, L., Pedersen, A. H., and Kisiel, W. (1989) J. Biol. Chem. 264, 9980-9988). In this study, we compare recombinant human factor VIIa and a preparation of recombinant human factor VIIa lacking the gamma-carboxyglutamic acid domain (GD-rVIIa) with respect to their interaction with J82 cell surface tissue factor. Interaction of GD-rVIIa with J82 monolayers at 37 degrees C was specific, saturable, and exhibited a hyperbolic profile. Scatchard plots of the binding data obtained at 37 degrees C indicated a single class of binding sites for GD-rVIIa with a Kd value of 2.5 nM. GD-rVIIa interacted with about 10,000 binding sites/cell. In contrast to the tissue factor-specific binding observed for intact factor VIIa, specific binding of GD-rVIIa to the J82 cell surface was neither influenced by calcium nor blocked by prior incubation of the cells with polyclonal anti-tissue factor apoprotein IgG. In addition, cell-bound GD-rVIIa failed to activate human factor X. These results indicate that the gamma-carboxyglutamic acid domain of factor VIIa is essential for its interaction with cell surface tissue factor.