Leishmaniasis, caused by Leishmania parasites, is an important public health problem worldwide. Leishmania, like other trypanosomatids, present unique biological features as compared to higher eukaryotes that can be exploited with the intent of finding new chemotherapeutical/vaccine candidates. Mechanisms of cellular sorting in Leishmania can be viewed as such potential targets. We have previously demonstrated a role for the pro-domain of a Leishmania cysteine proteinase in lysosomal targeting. In this paper, we show that this signal is not recognized by mammalian cells and is recognized by yeast; we also discuss here the implications of these findings related to evolution and further characterization of the Leishmania trafficking machinery.