Characteristics of plasminogen binding to Trypanosoma cruzi epimastigotes

The binding constants of the interaction between plasminogen and Trypanosoma cruzi epimastigotes were determined. An indirect method in which the bound plasminogen is detached from the cell by -aminocaproic acid and a direct method through biotinylated plasminogen were used. The analyses revealed a dissociation constant (Kd) from 0.4 to 1.2 μM, these values being compatible with recognition in vivo. Moreover, epimastigotes from the gut of Rhodnius prolixus were able to bind plasminogen from the blood meal. Fragments derived from elastase digestion of plasminogen were tested for their ability to bind T. cruzi cells. The fragment with highest ability to interact with the parasite was miniplasminogen that bound in a concentration-dependent and saturable manner with a Kd similar to that for plasminogen. This binding was inhibited by -aminocaproic acid indicating that the lysine-binding site of kringle 5 may be responsible for the interaction of plasminogen with T. cruzi.