Summary
The strategic position of factor Xa (FXa) in blood coagulation makes it a compelling
target for the development of new anticoagulants. Bloodsucking animals have in their
salivary glands mixtures of anticoagulants, which could be used for designing novel
antithrombotic compounds. Herein, we describe Vizottin, the first FXa inhibitor from
the salivary complex of the leech Haementeria vizottoi. Vizottin was purified by gel filtration and reverse-phase chromatography, and shown
to have anticoagulant effects in human plasma, prolonging the recalcification time
in a dose-dependent manner (IC50 40 nM). Vizottin induced blood incoagulability in
FX-deficient plasma, whereas in normal and reconstituted plasma, Vizottin doubled
the prothrombin time at 160 nM. This peptide competitively inhibited human FXa (Ki 2 nM) like FXa inhibitors from other leeches, albeit via a distinct mechanism of
action. At high concentrations, vizottin inhibited the amidolytic activity of factor
VIIa/tissue factor (IC50 96.4 nM). Vizottin inhibited FXa in the prothrombinase complex
and Gla-domainless FXa. Moreover, vizottin did not interfere with FX activation induced
by RVV-X, a known enzyme that requires the Gla-domain of FX for activation. Competition
experiments in the presence of FXa and GGACK-FXa (active site blocked) demonstrated
that the inhibition of FXa by vizottin is through binding to the active site rather
than an exosite. This novel inhibitor appears to exert its inhibitory effects through
direct binding to the active site of FXa in a time-dependent manner, but not involving
a tight-binding model. In this context, vizottin is a promising model for designing
novel anticoagulants for the treatment of thrombotic diseases.
Keywords
Leech salivary gland - Haementeria - factor Xa inhibitor - factor Xa active site -
extrinsic tenase complex