Cloning, nucleotide sequence and expression of the gene encoding factor Xainhibitor from the salivary glands of the tick, Ornithodoros savignyi

The N-terminal sequence of the competitive and slow tight-binding factor Xa inhibitor (fXaI; K-i = 0.83 +/- 0.10 nM) isolated from the salivary glands of Ornithodoros savignyi ticks (Acari: Argasidae) was employed to design a degenerate gene-specific primer (GSP) for 3'-rapid amplification of cDNA e nds (3'-RACE). The primer consisted of a sequence encoding for amino acid r esidues 5-11. A full-length gene was next constructed from the 3'-RACE prod uct in a two-step PCR procedure and successfully expressed by the BAC-TO-BA C baculovirus expression system. The deduced amino acid sequence of the gen e showed 46% identity and 78% homology to an fXaI (TAP) from Ornithodoros m oubata. Recombinant fXaI (rfXaI) consists of 60 amino acid residues, has a molecular mass of similar to 7 kDa and inhibited fXa by similar to 91%. The availability of the rfXaI will aid further investigations of its potential for therapeutic applications and as vaccine against tick infestation. The authentic nucleotide sequence of the gene encoding tick fXaI furthermore en ables studies at the genetic level and probing of other tick species for si milar and related genes. Exp Appl Acarol 22: 603-619 (C) 1998 Kluwer Academ ic Publishers.