Fibrin-targeted direct factor Xa inhibition: construction and characterization of a recombinant factor Xa inhibitor composed of an anti-fibrin single-chain antibody and tick anticoagulant peptide

SummaryWe investigated whether the direct fXa inhibitor tick anticoagulant peptide (TAP) can be N-terminally coupled to a clot-targeting, single-chain antibody specific for fibrin (scFv59D8). Due to its unique position at the convergence point of the intrinsic and extrinsic pathways early in the coagulation cascade, factor Xa (fXa) represents an attractive therapeutic target. In contrast to indirect inhibitors, direct fXa inhibitors effectively inhibit clotbound and prothrombinase-associated fXa. Targeting of direct fXa inhibitors to clots promises to enhance local anticoagulative potency and to reduce systemic anticoagulation which potentially results in less bleeding complications. TAP is a highly potent fXa inhibitor. Since its N-terminus is essential for antifXa activity, it was a challenging question, whether TAP will be active as a N-terminally coupled fusion molecule. Two step affinity chromatography with Ni2+ and β15-22-peptide of human fibrin results in a pure 36 kDa protein, which was tested for its targeting function and anti-fXa activity. The recombinant fusion did not destroy the function of the fusion partners. Antibody binding function was on a par with the parent molecule. TAP activity was partially reduced, arguing that a free N-terminus is not required for anti-fXa activity, but is important for maximal potency. In human whole blood clots, scFv59D8-TAP revealed anticoagulative properties at concentrations (200 to 500 nM) where non-targeted TAP did not reveal anticoagulative activity at all. In summary, scFv59D8-TAP constitutes a promising new anticoagulant with fibrin-targeted factor Xa inhibition. The production in E. coli and the established purification methods are a solid basis for a modern, large scale production at low cost and reproducible activity.

Crystallization and preliminary X-ray diffraction data of the complex of recombinant tick anticoagulant peptide (rTAP) and bovine factor Xa

The complex of bovine factor Xa and recombinant tick anticoagulant peptide (rTAP) was crystallized in two different crystal forms using polyethylene glycol as a precipitant. Form I belongs to space group P42212 with unit-cell dimensions a = b = 133.1, c = 68.8 Å. It contains one complex per asymmetric unit and diffracts to 3.0 Å resolution. Form II belongs to P41212 (or P43212) with dimensions a = b = 126.5, c = 146.7 Å; it contains two complexes per asymmetric unit and diffracts to 2.5 Å. The crystals of both forms consist of factor Xa (MW = 45.3 kDa) and rTAP (MW = 6.7 kDa).