Tissue factor pathway inhibitor: regulation of its inhibitory activity by phospholipid surfaces.
The basic C-terminus of Tissue Factor Pathway Inhibitor (TFPI) appears to be essential for its anticoagulant activity when tested in a diluted thromboplastin prothrombin time assay. Although the data reported so far have increased our knowledge about the C-terminus as a major binding site for heparin, lipoproteins and phospholipids, it is still unclear how this region of TFPI plays a role in its anticoagulant mode of action. We earlier reported that in the presence of phospholipid the rate of association of factor Xa with full length TFPI (FL-TFPI) is about 10-fold faster than with C-terminus truncated TFPI. This in turn makes that, in vitro, full length TFPI is a more potent inhibitor of tissue factor-factor VIIa catalyzed factor X activation than truncated TFPI. Binding studies, utilizing an ellipsometer, revealed that in contrast to the complex of C-terminus truncated TFPI (TFPI1-161) and factor Xa, the FL-TFPI.factor Xa complex has a high affinity for negatively charged phospholipids. However, when examined in a tubular flow reactor containing tissue factor embedded in a phospholipid bilayer composed of 25 mol% phosphatidyl-serine/75 mol% phosphatidylcholine, no differences in the potency of FL-TFPI and TFPI1-161 to inhibit factor X activation were found. The two variants of TFPI did show an interesting difference though. We found that the quaternary complex of TF.factor VIIa.FL-TFPI.factor Xa was much more stable than the complex containing TFPI1-161. This difference could not be attributed to their different phospholipid-binding properties since the same difference in stability was found on membranes that contained only DOPC.
Lindhout
T
T
Dept. of Biochemistry, University of Limburg, Maastricht, The Netherlands.
Salemink
I
I
Valentin
S
S
Willems
G M
GM
D001665:Binding Sites; D004789:Enzyme Activation / Q000187:drug effects; D015951:Factor Xa / Q000378:metabolism*; D006801:Humans; D008051:Lipid Bilayers; D008074:Lipoproteins / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D046911:Macromolecular Substances; D010446:Peptide Fragments / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism; D010743:Phospholipids / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D013499:Surface Properties
D008051:Lipid Bilayers; D008074:Lipoproteins; D046911:Macromolecular Substances; D010446:Peptide Fragments; D010713:Phosphatidylcholines; D010743:Phospholipids; C051928:lipoprotein-associated coagulation inhibitor; D015951:Factor Xa; C017251:1,2-oleoylphosphatidylcholine