The salivary gland of Ixodes scapularis has developed a repertoire of antihemostatic compounds that counteracts host defenses. Through massive sequencing of a cDNA library of the salivary gland of I. scapularis a clone of 498 nucleotides with sequence homology to tissue factor pathway inhibitor (TFPI) has been identified. This cDNA codes for a mature protein, herein called Ixolaris, with 140 amino acids containing ID cysteines and with a predicted pi of 4.56. Ixolaris is distinct from mammalian TFPI in functional and structural aspects. Ixolaris was expressed as an active recombinant molecule in insect cell lines and inhibits Factor VIIa/TF-induced Factor X activation with a K 0.5 of 6.73 pM. In addition, Ixolaris behaves as a fast-and-tight ligand of Factor Xa, enhancing its proteolytic activity - 2 fold toward chromogenic substrate (S2222). Ixolaris binds to Factor Xa but not to Factor X or Factor Vila, as assessed by native PAGE. In the presence of DEGR-Factor Xa, Ixolaris blocks Factor VIIa/TF proteolytic activity toward chromogenic substrate (S2288). In addition, Ixolaris inhibits in a dose-dependent manner thrombin formation by the prothrombinase assay and it increases prothrombin time. Ixolaris is the first and highly specific inhibitor for Factor VlIa/TF-mediated Factor X activation described in the salivary gland of a blood-sucking arthropod. Ixolaris may be useful as an anticoagulant for cardiovascular diseases as well as a vaccine target to prevent Lyme disease.
|Original language||English (US)|
|Issue number||11 PART I|
|State||Published - 2000|
ASJC Scopus subject areas
- Cell Biology