Interactions Outside the Proteinase-binding Loop Contribute Significantly to the Inhibition of Activated Coagulation Factor XII by Its Canonical Inhibitor from Corn

Abstract

Background: Canonical inhibitors interact with cognate proteases through a protease-binding loop.Results: Protease-binding loop of corn Hageman factor inhibitor (CHFI) does not inhibit its cognate enzyme-activated coagulation factor XII (FXIIa).Conclusion: Nonloop regions of CHFI are required for specific inhibition of FXIIa.Significance: CHFI is the first canonical inhibitor whose protease-binding loop is not sufficient for cognate enzyme inhibition.

Assessment of the protein interaction between coagulation factor XII and corn trypsin inhibitor by molecular docking and biochemical validation

“…These confirm the essential role of the canonical P1 residue Arg34, and establish for the first time the importance of the more remote residues Trp22 and Arg43 in CTI α‐helices 1 and 2. The docking solution is not consistent with a previously reported non‐canonical docking solution , which places CTI at a different location on the surface of FXIIa. Differences in the methodology between the two studies are that, in the current study, a hybrid model of the FXIIa structure was used as opposed to a purely HGFA‐derived homology model .…”

“…The docking solution is not consistent with a previously reported non‐canonical docking solution , which places CTI at a different location on the surface of FXIIa. Differences in the methodology between the two studies are that, in the current study, a hybrid model of the FXIIa structure was used as opposed to a purely HGFA‐derived homology model . It is likely that the accurate placement of FXIIa residue Asp60A in the hybrid FXIIa model plays a role in improving the docking as compared with the HGFA‐derived homology model.…”

“…It is likely that the accurate placement of FXIIa residue Asp60A in the hybrid FXIIa model plays a role in improving the docking as compared with the HGFA-derived homology model. However, the current canonical model is consistent with experimental observations that disruption of the cysteine loop structure of CTI affects its inhibition of FXII [29], whereby the function of the cysteine loops would primarily be to provide the three-dimensional context for the conformation of the inhibitory loop of CTI.…”

“…For thrombin and FXIa, a canonical docking pose with CTI was also observed, but only for CTI structure 1BEA, and inspection of these docking solutions revealed steric clashes. This is consistent with previous reports that CTI weakly inhibits FXIa and does not inhibit thrombin [14,29]. Of all the proteases investigated, FXIIa was the only canonical top-ranked docking solution for both CTI structures 1BFA and 1BEA, and the values of energy were more significant than with any of the other solutions in the study (Table S1).…”

Recent advances in the discovery and development of factor XI/XIa inhibitors

“…Several polypeptides have been reported to inhibit human FXIa. These include aprotinin (FXIa K i = 288 nM), corn Hageman factor inhibitor (FXIa K i = 5.4 μM), Desmolaris ( K i = 0.63 nM), ecotin and mutants, Fasxiator (FXIa K D = 20.2 nM), human placental bikunin (FXIa K i = 6 nM), Ixodes ricinus contact phase inhibitor, nematode proteins of AcaNAP10 (FXIa K i = 25.8 nM) and AduNAP4 (FXIa K i = 42.5 nM), protease nexin‐2 (PN‐2), simukunin (FXIa IC 50 = 56.7 nM), and tissue factor pathway inhibitor‐2 (also reported as KD1‐WT; FXIa K i = 15 nM) . Considering the specificity of these polypeptides, Desmolaris, Fasxiator, and PN‐2 are relatively the most interesting, and thus, are described in detail in the following sections.…”