A new Factor Xa inhibitor from Amblyomma cajennense with a unique domain composition.

Abstract Bioactive compounds of great interest are found in the saliva of hematophagous organisms. While exploring a cDNA library derived from the salivary glands of the tick Amblyomma cajennense , a transcript that codes for a protein with unique structure (containing an N-terminal Kunitz-type domain and a C-terminus with no homology to any annotated sequences) was found. The recombinant mature form of this protein (∼13.5 kDa) was produced in Escherichia coli BL21 (DE3), and it was able to inhibit Factor Xa (FXa) and extend global blood clotting times in vitro and ex vivo . Static and dynamic predictions of its tertiary structure indicate regions that may be related to its FXa inhibitor function.