**4. Conclusions**

The present work is the first of its kind to characterize the recombinant cystatin of leeches attained through the sequence of the transcript Hviz00340 from the transcriptome of *Haementeria vizottoi* [23]. Cystatin-Hv was successfully expressed in *Pichia pastoris,* and after purification, it was characterized for its ability to inhibit cathepsin L. Kinetic studies have indicated that recombinant Cystatin-Hv is a potent inhibitor of cathepsin L, with a Ki of 7.9 nM. Thus, a rigorous study of this molecule could be promising, and future work will be carried out in this direction to better characterize the therapeutic potential of Cystatin-Hv.
