Processing of metacaspase into a cytoplasmic catalytic domain mediating cell death in Leishmania major

Abstract

Metacaspases are cysteine peptidases that could play a role similar to caspases in the cell death programme of plants, fungi and protozoa. The human protozoan parasite Leishmania major expresses a single metacaspase (LmjMCA) harbouring a central domain with the catalytic dyad histidine and cysteine as found in caspases. In this study, we investigated the processing sites important for the maturation of LmjMCA catalytic domain, the cellular localization of LmjMCA polypeptides, and the functional role of the catalytic domain in the cell death pathway of Leishmania parasites. Although LmjMCA polypeptide precursor form harbours a functional mitochondrial localization signal (MLS), we determined that LmjMCA polypeptides are mainly localized in the cytoplasm. In stress conditions, LmjMCA precursor forms were extensively processed into soluble forms containing the catalytic domain. This domain was sufficient to enhance sensitivity of parasites to hydrogen peroxide by impairing the mitochondrion. These data provide experimental evidences of the importance of LmjMCA processing into an active catalytic domain and of its role in disrupting mitochondria, which could be relevant in the design of new drugs to fight leishmaniasis and likely other protozoan parasitic diseases.

Antagonic activities of Trypanosoma cruzi metacaspases affect the balance between cell proliferation, death and differentiation

“…We also showed for TcMCA5 that its C-terminal extension negatively regulates its ability to promote an apoptotic-like cell death based on its catalytic activity (Figures 2 and 5), suggesting that active TcMCA5 may have a pro-apoptotic role regulated by proteolytic processing of its C-terminal extension, as recently described for LmjMCA by Zalila et al 11 The observed difference in phenotypes for TcMCA5 and TcMCA5DCt overexpressors seems not to be due to a different subcellular distribution of the protein (data not shown), but could be attributed to an enhanced activity, as the artificial deletion of the C-terminal extension in TcMCA5 increases its catalytic efficiency by 2.7-fold. On the other hand, the C terminus might maintain the protein in a different conformation, preventing the cleavage activation of proapoptotic proteins.…”

“…5 Their substrate specificity is for basic residues at P1 position, making them unable to cleave caspase substrates. 6 Evidences suggest that metacaspases modulate cell death, [7][8][9][10][11] cell cycle progression [12][13][14] and protein aggregation, 15 but there is still controversy about their functions and their relation with caspases. [16][17][18] The fact that metacaspases are not present in humans and fulfil important roles in trypanosomatids make them attractive drug targets, and a first series of inhibitors with trypanocidal activity has been developed recently.…”

Crystal structure of a Trypanosoma brucei metacaspase

“…In plants, metacaspases are essential for embryogenesis (5, 6) and have been shown to act in antagonistic relationships, functioning as both positive and negative regulators of PCD (7). In yeast and some protozoa, metacaspases have been implicated as mediators of cell death in response to oxidative stress and environmental change (3,(8)(9)(10).Various attempts have been made to draw parallels between caspases and metacaspases in respect to structure, activation, and function (11). However, two striking differences between metacaspases and caspases are their substrate specificities and requirements for activation.…”

“…In plants, metacaspases are essential for embryogenesis (5, 6) and have been shown to act in antagonistic relationships, functioning as both positive and negative regulators of PCD (7). In yeast and some protozoa, metacaspases have been implicated as mediators of cell death in response to oxidative stress and environmental change (3,(8)(9)(10).…”

“…It is now apparent, however, that metacaspases have a variety of cellular functions that are distinct from those of the caspases, which may reflect the distinct differences in substrate specificity and activation (11). For example, in yeast, the Yca1 metacaspase is required for clearance of cellular protein aggregates as well as regulation of the timing of the cell cycle, a function that has also been identified in the parasitic protozoon Leishmania (9,(17)(18)(19).…”