TSETSE THROMBIN INHIBITOR - BLOODMEAL-INDUCED EXPRESSION OF AN ANTICOAGULANT IN SALIVARY-GLANDS AND GUT TISSUE OF GLOSSINA-MORSITANS MORSITANS

The tsetse thrombin inhibitor, a potent and specific low molecular mas s (3,530 Da) anticoagulant peptide, was purified previously from saliv ary gland extracts of Glossina morsitans morsitans (Diptera: Glossinid ae). A 303-bp coding sequence corresponding to the inhibitor has now b een isolated from a tsetse salivary gland cDNA library by using degene rate oligonucleotide probes. The full-length cDNA contains a 26-bp unt ranslated segment at its 5' end, followed by a 63-bp sequence correspo nding to a putative secretory signal peptide. A 96-bp segment codes fo r the mature tsetse thrombin inhibitor, whose predicted molecular weig ht matches that of the purified native protein. Based on its lack of h omology to any previously described family of molecules, the tsetse th rombin inhibitor appears to represent a unique class of naturally occu rring protease inhibitors. Recombinant tsetse thrombin inhibitor expre ssed in Escherichia coli and the chemically synthesized peptide are bo th substantially less active than the purified native protein, suggest ing that posttranslational modification(s) may be necessary for optima l inhibitory activity. The tsetse thrombin inhibitor gene, which is pr esent as a single copy in the tsetse genome, is expressed at high leve ls in salivary glands and midguts of adult tsetse flies, suggesting a possible role for the anticoagulant in both feeding and processing of the bloodmeal.