Fusion of two distinct peptide exosite inhibitors of Factor VIIa

Highly potent bifunctional inhibitors of Factor VIIa (FVIIa) were generated by linking two distinct peptides, recently shown to bind to two discrete exosites on the FVIIa protease domain [Dennis, Eigenbrot, Skelton, Ultsch, Santell, Dwyer, O'Connell and Lazarus (2000) Nature (London) 404, 465-470; Dennis, Roberge, Quan and Lazarus (2001) Biochemistry 40, 9513-9521; Roberge, Santell, Dennis, Eigenbrot, Dwyer and Lazarus (2001) Biochemistry 40, 9522-9531]. Fusion peptides consisting of an N-terminal A-series peptide followed by flexible linkers, an E-series peptide, and the Z-domain of protein A were expressed in Escherichia coli and purified using IgG-Sepharose affinity chromatography. The fusion peptides were potent anticoagulants and had steep concentration dependence curves in tissue factor-dependent prothrombin time (PT) assays in comparison to the individual peptides or their noncovalent combination. This phenomenon was dependent on the length of the linker joining the A- and E-peptides. The fusion of the peptides increased the extent of inhibition of Factor X (FX) activation to 100% at saturating peptide concentrations, but did not improve the binding affinity for Factor VIIa (FVIIa) at the A- and E- binding sites or the IC(50) for the inhibition of FX activation. Differences between the peptides in the PT fold prolongation in normal and FVII-deficient plasma, in conjunction with the inhibition of (125)I-FVII activation, suggest that the enhanced effects of the fusion peptides involve the inhibition of FVII autoactivation.