Processing and trafficking of cysteine proteases in Leishmania mexicana

Removal of the pro-domain of a cysteine protease is essential for activatio n of the enzyme. We have engineered a cysteine protease (CPB2.8) of the pro tozoan parasite Leishmania mexicana by site-directed mutagenesis to remove the active site cysteine (to produce CPBC25G). When CPBC25G was expressed i n a L, mexicana mutant lacking all CPB genes, the inactive pro-enzyme was p rocessed to the mature protein and trafficked to the lysosome. These result s show that auto-activation is not required for correct processing of CPB i n vivo. When CPBC25G was expressed in a L. mexicana mutant lacking both CPA and CPB genes, the majority of the pro-enzyme remained unprocessed and acc umulated in the flagellar pocket. These data reveal that CPA can directly o r indirectly process CPBC25G and suggest that cysteine proteases are target ed to lysosomes via the flagellar pocket. Moreover, they show that another protease can process CPB in the absence of either CPA air CPB, albeit less efficiently. Abolition of the glycosylation site in the mature domain of CP B did not affect enzyme processing, targeting or in vitro activity towards gelatin. This indicates that glycosylation is not required for trafficking. Together these findings provide evidence that the major route of trafficki ng of Leishmania cysteine proteases to lysosomes is via the flagellar pocke t and therefore differs significantly from cysteine protease trafficking in mammalian cells.