Zinc (II) selectively enhances the inhibition of coagulation factor XIa by protease nexin-2/amyloid β-Protein precursor

Abstract

Protease nexin-2 (PN-2) is the secreted isoform of the Alzheimer's Amyloid β-Protein Precursor (AßPP) that contains the Kunitz-type protease inhibitor (KPI) domain. PN-2 AßPP is a potent inhibitor of coagulation factor XIa (FXIa) and is secreted in large quantities by activated platelets suggesting a normal function in regulating this protease at sites of vascular injury. In the present study, the effect of Zn 2+ on the protease inhibitory properties of PN-2 AßPP was quantitatively investigated. Zn 2+ (1 μM to 1 mM) had no effect on the inhibition of trypsin or chymotrypsin by PN-2 AßPP . In contrast, Zn 2+ at concentrations >1 μM increased the inhibition of FXIa by PN-2 AßPP . Enhancement of FXIa inhibition was virtually saturated at ≈100 μM Zn 2+ resulting in a final K i ≈ 6.0 × 10 −11 M. Zn 2+ had no effect on the inhibition of FXIa by a purified, recombinant KPI domain of PN-2 AßPP indicating that the native protein is required for the potentiation of FXIa inhibition. Heparin and Zn 2+ were found to further augment each other's ability to stimulate the inhibition of FXIa by PN-2 AßPP . Together, these findings suggest that the interaction of Zn 2+ with PN-2 AßPP may be important for optimal inhibition of FXIa.