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Tissue factor (TF), an initiator of blood coagulation in vivo, is expressed in a variety of cells. Sufficient natural TF has been isolated to clone and express recombinant proteins ranging from full-length TF to its extracellular domain. Because of the limited availability of natural TF, recombinant proteins have been used as surrogates. Despite the differences in their post-translational modifications, it has been accepted that membrane-anchored recombinant TFs are quite similar to the natural TF. Recent studies, however, have shown that post-translational modifications play an important role in TF-triggered thrombin generation.

Background: Tissue factor (TF) is a single polypeptide integral membrane glycoprotein composed of 263 residues and is essential to life in its role as the initiator of blood coagulation. Previously we have shown that the activity of the natural placental TF (pTF) and the recombinant TF (rTF) from Sf9 insect cells is different (Krudysz-Amblo, J. et al (2010) J. Biol. Chem. 285, 3371-3382)., Methods: In this study, using mass spectrometry, we show by quantitative analysis that the extent of glycosylation varies on each protein., Results and Conclusions: Fractional abundance of each glycan composition at each of the three glycosylation sites reveals the most pronounced difference to be at asparagine (Asn) 11. This residue is located in the region of extensive TF-factor VIIa (FVIIa) interaction. Carbohydrate fractional abundance at Asn11 revealed that glycosylation in the natural placental TF is much more prevalent (~76%) than in the recombinant protein (~20%). The extent of glycosylation on Asn124 and Asn137 is similar in the two proteins, despite the pronounced differences in the carbohydrate composition. Additionally, 77% of rTF exists as TF des-1, 2 (missing the first two amino acids from the N-terminus). In contrast, only 31% of pTF is found in the des-1, 2 form., Conclusion: These observations may attribute to the difference in the ability of TF-FVIIa complex to activate factor X (FX)., General Significance: Structural and functional comparison of the recombinant and natural protein advances our understanding and knowledge on the biological activity of TF., (2010 Elsevier B.V. All rights reserved.)

Tissue factor is a membrane protein, which in a complex with factor VIIa initiates in vivo blood coagulation. Due to the scarcity of natural tissue factor protein, most studies have relied upon recombinant tissue factor forms. However, there have been only cursory experimental comparisons of natural and recombinant tissue factor proteins. Our preliminary data suggested that placental tissue factor in a complex with factor VIIa was more efficient activator of factor X than the recombinant protein. After deglycosylation, both forms of tissue factor showed almost an identical activity in the extrinsic factor Xase. Analyses using tryptic digestion and mass-spectrometry revealed that the levels of glycosylation and the composition of carbohydrates present in natural placental tissue factor were different than those in its recombinant counterpart. These data indicate that natural and recombinant tissue factor proteins differ in their posttranslational modifications and that these differences translate into different cofactor activity. Thus the use of recombinant tissue factor proteins for the quantitation of natural tissue factor is misleading., (Copyright (c) 2009 Elsevier Ltd. All rights reserved.)

The effect of glycosylation on tissue factor (TF) activity was evaluated, and site-specific glycosylation of full-length recombinant TF (rTF) and that of natural TF from human placenta (pTF) were studied by liquid chromatography-tandem mass spectrometry. The amidolytic activity of the TF.factor VIIa (FVIIa) complex toward a fluorogenic substrate showed that the catalytic efficiency (V(max)) of the complex increased in the order rTF(1-243) (Escherichia coli) < rTF(1-263) (Sf9 insect cells) < pTF for the glycosylated and deglycosylated forms. Substrate hydrolysis was unaltered by deglycosylation. In FXase, the K(m) of FX for rTF(1-263)-FVIIa remained unchanged after deglycosylation, whereas the k(cat) decreased slightly. A pronounced decrease, 4-fold, in k(cat) was observed for pTF.FVIIa upon deglycosylation, whereas the K(m) was minimally altered. The parameters of FX activation by both rTF(1-263D)-FVIIa and pTF(D)-FVIIa were identical and similar to those for rTF(1-243)-FVIIa. In conclusion, carbohydrates significantly influence the activity of TF proteins. Carbohydrate analysis revealed glycosylation on asparagines 11, 124, and 137 in both rTF(1-263) and pTF. The carbohydrates of rTF(1-263) contain high mannose, hybrid, and fucosylated glycans. Natural pTF contains no high mannose glycans but is modified with hybrid, highly fucosylated, and sialylated sugars.