The Kunitz 1 and Kunitz 3 domains of tissue factor pathway inhibitor are required for efficient inhibition of factor Xa

Sameera Peraramelli, Dennis P. L. Suylen, Jan Rosing, Tilman M. Hackeng*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


Tissue factor pathway inhibitor (TFPI) is a slow tight-binding inhibitor that inhibits factor (F)Xa in a biphasic fashion: a rapid formation of loose FXa.TFPI encounter complex is followed by slow rearrangement into a tight FXa.TFPI* complex in which the Kunitz-2 (K2) domain of TFPI binds and inhibits FXa. In the current study, full-length TFPI (TFPIfl) and various truncated TFPI constructs were used to assess the importance of TFPI domains other than K2 in the inhibition of FXa. In the absence of Ca2+ ions, FXa was more effectively inhibited by TFPIfl than Gla-domain less FXa. In turn, Ca2+ ions impaired FXa inhibition by TFPIfl but not by TFPI constructs that lack the C-terminus. This suggests that, in absence of Ca2+ ions, interactions between the C-terminus of TFPI and the Gla-domain of FXa promote FXa-inhibition. TFPIfl and K2K3 had similar efficiencies for encounter complex formation. However, K2K3 showed monophasic inhibition instead of biphasic inhibition, indicating absence of rearrangement into a tight complex. K1K2 and TFPI1-161 showed biphasic inhibition, but had less efficient encounter complex formation than TFPIfl. Finally, K2K3 was a 10-fold more efficient FXa-inhibitor than K2. These results indicate that K3-C-terminus enhances the formation of encounter complex and that K1 is required for isomerisation of the encounter- into tight complex. Since TFPIfl has a 10-fold higher Ki than K2K3-C-terminus, we propose that K1 is not only required for the transition of the loose to the tight FXa.TFPI* complex, but also inhibits FXa.TFPI encounter complex formation. This inhibitory activity is counteracted by K3 and C-terminus.
Original languageEnglish
Pages (from-to)266-276
JournalThrombosis and Haemostasis
Issue number2
Publication statusPublished - Aug 2012


  • Anticoagulant
  • TFPI
  • protein S
  • factor Xa


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