DISCONTINUED
DOMAIN STRUCTURE OF THROMBOMODULIN
The domain structure of thrombomodulin is represented, where: EGF = regions containing sequence homologous to human epidermal growth factor, O-GLYCOS = region rich in O-glycosylation sites, MEM = membrane spanning region, CYTO = cytoplasmic domain containing a free cycteine.
Properties of Thrombomodulin
| Localization: | Endothelial cell membrane, traces of degraded, yet functional, TM detected in human urine and plasma | |||||
| Mode of action: | Cofactor; enhances the proteolytic activation of protein C by thrombin | |||||
| Molecular weight: | 74,000 | |||||
| Extinction coefficient: |
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| Isoelectric point: | 2.5 | |||||
| Structure: | Single chain, NH2-terminal hydrophobic domain, six EGF domains, one O-glycosylation rich domain, one transmembrane domain, COOH-terminal cytoplasmic domain | |||||
| Post-translational modifications: | β-hydroxyasparagine (0.5 mol/mol of protein) |
20 mM Tris, 150 mM NaCl, 0.05% PDOC, pH 7.4
>95% by SDS-PAGE
NOT tissue/cell culture grade. Not tested for endotoxin.
Protein C activation assay
Storage
-80°C
Shelf Life (properly stored)
12 months
Overview of Thrombomodulin
Thrombomodulin (TM) is an integral membrane glycoprotein expressed on the surface of endothelial cells. Its discovery by Esmon and Owen has focused attention on the importance of the protein C anticoagulant pathway. TM serves as a cofactor for protein C activation by forming a 1:1 stoichiometric complex with thrombin (Kd=10-10M), which accelerates the rate of protein C activation by 1000-fold relative to the rate with thrombin alone. In addition to facilitating protein C activation, the binding of thrombin to TM drastically alters the procoagulant activity of thrombin. When bound to TM, thrombin no longer clots fibrinogen, activates factor V, inactivates protein S or triggers platelet aggregation.
TM is a single chain protein composed of 5 distinct domains. The domain structure of TM is similar to the low density lipoprotein (LDL) receptor. A short cytoplasmic domain containing a free cysteine is located at the COOH-terminal end and is joined by a membrane spanning region to an O-glycosylation rich domain. The latter is followed by an epidermal growth factor (EGF) homology region and the NH2-terminal hydrophobic domain. The EGF homology region contains 6 EGF-like domains and contains the binding sites for both thrombin and protein C.
Thrombomodulin is isolated from rabbit lung by a modification of the procedure described by Galvin et al. and is supplied as an aqueous solution in 0.02 M Tris, 0.15 M NaCl, pH 7.4, containing 0.05 % polidocanol, and can be stored at -80°C for up to a year. Purity is determined by SDS-PAGE analysis and activity is determined using a chromogenic assay for protein C activation.