PURIFICATION AND CHARACTERIZATION OF A MIDGUT LECTIN-TRYPSIN COMPLEX FROM THE TSETSE-FLY GLOSSINA-LONGIPENNIS

A blood-meal-induced lectin (agglutinin) with proteolytic activity was isolated from midgut extracts of Glossina longipennis by a two-step p rocedure involving anion-exchange chromatography. It is a glycoprotein [native molecular weight (M(r), 61000+/-3000 da) composed of two nonc ovalently-linked subunits designated alpha (M(r), similar to 27000 da) and beta (M(r), similar to 33000 da). The trypsin activity and the gl ycosyl residues were present on the alpha- and beta-subunits, respecti vely The native protein was capable of agglutinating both bloodstream- form and procyclic trypanosomes as well as rabbit red blood cells. Thi s activity was strongly inhibited by D-glucosamine and weakly inhibite d by N-acetyl-D-glucosamine. Similarly, soybean trypsin inhibitor abro gated agglutination of bloodstream-form parasites, whereas the procycl ics were unaffected. The agglutination activity was sensitive to tempe ratures above 40 degrees C but was unaffected by chelators of metal io ns. Antibodies raised against the protein were used in immunoblotting experiments to show the presence of a similar protein in several membe rs of the Glossina species. However, no cross-reactivity was detected with midgut extracts prepared from sandflies, mosquitoes, or stable fl ies. It is proposed that this molecule might play an important role in differentiation of bloodstream-form trypanosomes into procyclic (midg ut) forms.