Complementary DNA sequencing of canine tissue factor pathway inhibitor reveals a unique nanomeric repetitive sequence between the second and third Kunitz domains.

Tissue factor pathway inhibitor (TFPI) is a factor Xa-dependent inhibitor of the factor VIIa-tissue factor complex of blood coagulation. The primary amino acid sequence of canine TFPI has been deduced from cDNA sequences obtained using the techniques of reverse transcription followed by amplification using PCR and conventional screening of a canine endothelial cell cDNA library. The open reading frame for canine TFPI encodes a signal peptide of 28 amino acids followed by a 40.7 kDa protein of 368 amino acids. Similar to human, rat and rabbit TFPI, canine TFPI contains a negatively-charged cluster of amino acids at its mature amino-terminus, followed by three Kunitz-type proteinase inhibitory domains and a cluster of positively-charged amino acids near its carboxy-terminus. In contrast to other TFPIs, following its second Kunitz-type proteinase inhibitory domain canine TFPI contains an additional amino acid insert which includes a nanomeric peptide-sequence repeated six times. Recombinant canine TFPI was expressed in both bacterial- and insect cell-expression systems for functional analysis and the generation of antibodies. The recombinant canine TFPI inhibits tissue factor-induced coagulation in an in vitro canine system. Immunoprecipitation of TFPI from canine plasma, followed by Western-blot analysis, tentatively identifies canine TFPI as an 80,000 kDa protein. Anti-peptide antibodies raised to the nanomeric peptide repeat immunoprecipitate an identical, cross-reactive, 80,000 kDa protein.