The functional role of the autolysis loop in the regulation of factor X upon hemostatic response. (3rd January 2022)

• Record Type: Journal Article
• Authors: Bonde, Amalie Carnbring; Lund, Jacob; Hansen, Jens Jacob; Winther, Jakob Rahr; Nielsen, Per Franklin; Zahn, Stefan; Tiainen, Peter; Olsen, Ole Hvilsted; Petersen, Helle Heibroch; Bjelke, Jais Rose
• Is Part Of: Journal of thrombosis and haemostasis. Volume 20:Number 3(2022)
• Page Start: 589
• Page End: 599
• Publication Date: 2022-01-03
• Subjects: factor X -- glycosylation -- hemostasis -- site‐directed mutagenesis -- thrombin; Thrombosis -- Periodicals; Hemostasis -- Periodicals; Blood coagulation disorders -- Periodicals; 616.1
• DOI: 10.1111/jth.15624
• Languages: English
• ISSNs: 1538-7933

Abstract

Abstract: Background: The regulation of factor X (FX) is critical to maintain the balance between blood coagulation and fluidity. Objectives: To functionally characterize the role of the FX autolysis loop in the regulation of the zymogen and active form of FX. Methods: We introduced novel N‐linked glycosylations on the surface‐exposed loop spanning residues 143–150 (chymotrypsin numbering) of FX. The activity and inhibition of recombinant FX variants was quantified in pure component assays. The in vitro thrombin generation potential of the FX variants was evaluated in FX‐depleted plasma. Results: The factor VIIa (FVIIa)‐mediated activation and prothrombin activation was reduced, presumably through steric hinderance. Prothrombin activation was, however, recovered in presence of cofactor factor Va (FVa) despite a reduced prothrombinase assembly. The introduced N‐glycans exhibited position‐specific effects on the interaction with two FXa inhibitors: tissue factor pathway inhibitor (TFPI) and antithrombin (ATIII). Ki for the inhibition by full‐length TFPI of these FXa variants was increased by 7‐ to 1150‐fold, whereas ATIII inhibition in the presence of the heparin‐analog Fondaparinux was modestly increased by 2‐ to 15‐fold compared with wild‐type. When supplemented in zymogen form, the FX variants exhibited reduced thrombin generation activity relative to wild‐type FX, whereas enhanced procoagulant activity was measured for activated FXa variants. Conclusion: The autolysis loop participates in all aspects of FX regulation. In plasma‐based assays, a modest decrease in FX activation rate appeared to knock down the procoagulant response even when down regulation of FXa activity by inhibitors was reduced.