Posttranslational modifications of tissue factor

Abstract

Tissue factor (TF), a membrane protein, is an initiator of blood coagulation in vivo. In this review we discuss how posttranslational modifications affect activity and other properties of TF. Glycosylation of the extracellular domain and the composition of carbohydrates at three glycosylation sites have an influence on TF activity in the extrinsic FXase by increasing the rate of FX proteolysis. No influence of TF glycosylation on the activity of the FVIIa/TF complex towards small synthetic substrates was observed, suggesting that glycosylation has no effect on TF interaction with FVIIa. There are no published data suggesting a direct influence of phosphorylation or palmitoylation in the cytoplasmic domain on TF procoagulant activity. There has been a debate in the recent literature related to the role and formation of the Cys¹⁸⁶-Cys²⁰⁹ disulfide bond. Published opinions from various laboratories range from this bond being essential for the expression of cell TF activity to having no role in it. Overall, it is clear that some modifications of TF have an effect on TF procoagulant activity, signaling functions and trafficking. The influences of other modifications are debatable.

Figure 1

Amidolytic activity of FVIIa in complex with placental TF (pTF; diamonds) and recombinant full-length TF (rTF_1–263; squares) both glycosylated (G; filled symbols) and deglycosylated (D; open symbols). Increasing concentrations of TF were incubated with 0.5 nM FVIIa followed by the addition of 50 µM fluorogenic substrate. The rate of substrate hydrolysis was recorded. From J Biol Chem 2010;285:3371–82 (26).

Figure 2

Proteolytic activity of the extrinsic FXase formed by FVIIa and relipidated placental TF (◆ glycosylated and ◊ deglycosylated), full-length recombinant TF_1–263 (■ glycosylated and □ deglycosylated) and truncated recombinant TF_1–243 (● native and ○ “deglycosylated”). FVIIa (5 nM) was incubated with 0.1 nM relipidated TF and increasing concentrations of FX were added. FXa generation was monitored in a chromogenic assay. From J Biol Chem 2010;285:3371–82 (26).